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https://github.com/mainmatter/100-exercises-to-learn-rust
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.github/workflows/ci.yml
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- main
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- main
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jobs:
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jobs:
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formatter:
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runs-on: ubuntu-latest
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steps:
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- uses: actions/checkout@v3
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- uses: dprint/check@v2.2
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check-links:
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check-links:
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runs-on: ubuntu-latest
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runs-on: ubuntu-latest
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steps:
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steps:
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10
README.md
10
README.md
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@ -1,15 +1,15 @@
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# Learn Rust, one exercise at a time
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# Learn Rust, one exercise at a time
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You've heard about Rust, but you never had the chance to try it out?
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You've heard about Rust, but you never had the chance to try it out?\
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This course is for you!
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This course is for you!
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|
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You'll learn Rust by solving 100 exercises.
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You'll learn Rust by solving 100 exercises.\
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You'll go from knowing nothing about Rust to being able to start
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You'll go from knowing nothing about Rust to being able to start
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writing your own programs, one exercise at a time.
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writing your own programs, one exercise at a time.
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|
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> [!NOTE]
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> [!NOTE]
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> This course has been written by [Mainmatter](https://mainmatter.com/rust-consulting/).
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> This course has been written by [Mainmatter](https://mainmatter.com/rust-consulting/).\
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> It's one of the trainings in [our portfolio of Rust workshops](https://mainmatter.com/services/workshops/rust/).
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> It's one of the trainings in [our portfolio of Rust workshops](https://mainmatter.com/services/workshops/rust/).\
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||||||
> Check out our [landing page](https://mainmatter.com/rust-consulting/) if you're looking for Rust consulting or
|
> Check out our [landing page](https://mainmatter.com/rust-consulting/) if you're looking for Rust consulting or
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||||||
> training!
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> training!
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||||||
|
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@ -20,7 +20,7 @@ to get started with the course.
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|
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## Requirements
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## Requirements
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|
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- **Rust** (follow instructions [here](https://www.rust-lang.org/tools/install)).
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- **Rust** (follow instructions [here](https://www.rust-lang.org/tools/install)).\
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If `rustup` is already installed on your system, run `rustup update` (or another appropriate command depending on how
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If `rustup` is already installed on your system, run `rustup update` (or another appropriate command depending on how
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||||||
you installed Rust on your system)
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you installed Rust on your system)
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to make sure you're running on the latest stable version.
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to make sure you're running on the latest stable version.
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|
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@ -2,28 +2,28 @@
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Welcome to **"100 Exercises To Learn Rust"**!
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Welcome to **"100 Exercises To Learn Rust"**!
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|
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This course will teach you Rust's core concepts, one exercise at a time.
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This course will teach you Rust's core concepts, one exercise at a time.\
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You'll learn about Rust's syntax, its type system, its standard library, and its ecosystem.
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You'll learn about Rust's syntax, its type system, its standard library, and its ecosystem.
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|
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We don't assume any prior knowledge of Rust, but we assume you know at least
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We don't assume any prior knowledge of Rust, but we assume you know at least
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another programming language.
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another programming language.\
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We also don't assume any prior knowledge of systems programming or memory management. Those
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We also don't assume any prior knowledge of systems programming or memory management. Those
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topics will be covered in the course.
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topics will be covered in the course.
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|
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In other words, we'll be starting from scratch!
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In other words, we'll be starting from scratch!\
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You'll build up your Rust knowledge in small, manageable steps.
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You'll build up your Rust knowledge in small, manageable steps.
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By the end of the course, you will have solved ~100 exercises, enough to
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By the end of the course, you will have solved ~100 exercises, enough to
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feel comfortable working on small to medium-sized Rust projects.
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feel comfortable working on small to medium-sized Rust projects.
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||||||
|
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## Methodology
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## Methodology
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|
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This course is based on the "learn by doing" principle.
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This course is based on the "learn by doing" principle.\
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It has been designed to be interactive and hands-on.
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It has been designed to be interactive and hands-on.
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|
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[Mainmatter](https://mainmatter.com/rust-consulting/) developed this course
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[Mainmatter](https://mainmatter.com/rust-consulting/) developed this course
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||||||
to be delivered in a classroom setting, over 4 days: each attendee advances
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to be delivered in a classroom setting, over 4 days: each attendee advances
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through the lessons at their own pace, with an experienced instructor providing
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through the lessons at their own pace, with an experienced instructor providing
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||||||
guidance, answering questions and diving deeper into the topics as needed.
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guidance, answering questions and diving deeper into the topics as needed.\
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||||||
If you're interested in attending one of our training sessions, or if you'd like to
|
If you're interested in attending one of our training sessions, or if you'd like to
|
||||||
bring this course to your company, please [get in touch](https://mainmatter.com/contact/).
|
bring this course to your company, please [get in touch](https://mainmatter.com/contact/).
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||||||
|
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@ -35,11 +35,11 @@ also find solutions to all exercises in the
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## Structure
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## Structure
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|
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On the left side of the screen, you can see that the course is divided into sections.
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On the left side of the screen, you can see that the course is divided into sections.
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Each section introduces a new concept or feature of the Rust language.
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Each section introduces a new concept or feature of the Rust language.\
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To verify your understanding, each section is paired with an exercise that you need to solve.
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To verify your understanding, each section is paired with an exercise that you need to solve.
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You can find the exercises in the
|
You can find the exercises in the
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[companion GitHub repository](https://github.com/mainmatter/100-exercises-to-learn-rust).
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[companion GitHub repository](https://github.com/mainmatter/100-exercises-to-learn-rust).\
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Before starting the course, make sure to clone the repository to your local machine:
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Before starting the course, make sure to clone the repository to your local machine:
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|
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```bash
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```bash
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@ -80,7 +80,7 @@ Run the `wr` command to start the course:
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wr
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wr
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```
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```
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`wr` will verify the solution to the current exercise.
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`wr` will verify the solution to the current exercise.\
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Don't move on to the next section until you've solved the exercise for the current one.
|
Don't move on to the next section until you've solved the exercise for the current one.
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|
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> We recommend committing your solutions to Git as you progress through the course,
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> We recommend committing your solutions to Git as you progress through the course,
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@ -95,10 +95,10 @@ Enjoy the course!
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## Author
|
## Author
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|
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This course was written by [Luca Palmieri](https://www.lpalmieri.com/), Principal Engineering
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This course was written by [Luca Palmieri](https://www.lpalmieri.com/), Principal Engineering
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Consultant at [Mainmatter](https://mainmatter.com/rust-consulting/).
|
Consultant at [Mainmatter](https://mainmatter.com/rust-consulting/).\
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Luca has been working with Rust since 2018, initially at TrueLayer and then at AWS.
|
Luca has been working with Rust since 2018, initially at TrueLayer and then at AWS.\
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Luca is the author of ["Zero to Production in Rust"](https://zero2prod.com),
|
Luca is the author of ["Zero to Production in Rust"](https://zero2prod.com),
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the go-to resource for learning how to build backend applications in Rust.
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the go-to resource for learning how to build backend applications in Rust.\
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He is also the author and maintainer of a variety of open-source Rust projects, including
|
He is also the author and maintainer of a variety of open-source Rust projects, including
|
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[`cargo-chef`](https://github.com/LukeMathWalker/cargo-chef),
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[`cargo-chef`](https://github.com/LukeMathWalker/cargo-chef),
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[Pavex](https://pavex.dev) and [`wiremock`](https://github.com/LukeMathWalker/wiremock-rs).
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[Pavex](https://pavex.dev) and [`wiremock`](https://github.com/LukeMathWalker/wiremock-rs).
|
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@ -2,16 +2,16 @@
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|
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<div class="warning">
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<div class="warning">
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|
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Don't jump ahead!
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Don't jump ahead!\
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Complete the exercise for the previous section before you start this one.
|
Complete the exercise for the previous section before you start this one.\
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||||||
It's located in `exercises/01_intro/00_welcome`, in the [course GitHub's repository](https://github.com/mainmatter/100-exercises-to-learn-rust).
|
It's located in `exercises/01_intro/00_welcome`, in the [course GitHub's repository](https://github.com/mainmatter/100-exercises-to-learn-rust).\
|
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Use [`wr`](00_welcome.md#wr-the-workshop-runner) to start the course and verify your solutions.
|
Use [`wr`](00_welcome.md#wr-the-workshop-runner) to start the course and verify your solutions.
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</div>
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</div>
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|
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The previous task doesn't even qualify as an exercise, but it already exposed you to quite a bit of Rust **syntax**.
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The previous task doesn't even qualify as an exercise, but it already exposed you to quite a bit of Rust **syntax**.
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We won't cover every single detail of Rust's syntax used in the previous exercise.
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We won't cover every single detail of Rust's syntax used in the previous exercise.
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Instead, we'll cover _just enough_ to keep going without getting stuck in the details.
|
Instead, we'll cover _just enough_ to keep going without getting stuck in the details.\
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One step at a time!
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One step at a time!
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|
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## Comments
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## Comments
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@ -88,7 +88,7 @@ It is considered idiomatic to omit the `return` keyword when possible.
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|
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### Input parameters
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### Input parameters
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|
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Input parameters are declared inside the parentheses `()` that follow the function's name.
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Input parameters are declared inside the parentheses `()` that follow the function's name.\
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Each parameter is declared with its name, followed by a colon `:`, followed by its type.
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Each parameter is declared with its name, followed by a colon `:`, followed by its type.
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|
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For example, the `greet` function below takes a `name` parameter of type `&str` (a "string slice"):
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For example, the `greet` function below takes a `name` parameter of type `&str` (a "string slice"):
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@ -105,10 +105,10 @@ If there are multiple input parameters, they must be separated with commas.
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|
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### Type annotations
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### Type annotations
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Since we've been mentioned "types" a few times, let's state it clearly: Rust is a **statically typed language**.
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Since we've been mentioned "types" a few times, let's state it clearly: Rust is a **statically typed language**.\
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Every single value in Rust has a type and that type must be known to the compiler at compile-time.
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Every single value in Rust has a type and that type must be known to the compiler at compile-time.
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|
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Types are a form of **static analysis**.
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Types are a form of **static analysis**.\
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You can think of a type as a **tag** that the compiler attaches to every value in your program. Depending on the
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You can think of a type as a **tag** that the compiler attaches to every value in your program. Depending on the
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tag, the compiler can enforce different rules—e.g. you can't add a string to a number, but you can add two numbers
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tag, the compiler can enforce different rules—e.g. you can't add a string to a number, but you can add two numbers
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together.
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together.
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@ -1,6 +1,6 @@
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# A Basic Calculator
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# A Basic Calculator
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|
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In this chapter we'll learn how to use Rust as a **calculator**.
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In this chapter we'll learn how to use Rust as a **calculator**.\
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It might not sound like much, but it'll give us a chance to cover a lot of Rust's basics, such as:
|
It might not sound like much, but it'll give us a chance to cover a lot of Rust's basics, such as:
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|
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- How to define and call functions
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- How to define and call functions
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# Types, part 1
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# Types, part 1
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In the ["Syntax" section](../01_intro/01_syntax.md) `compute`'s input parameters were of type `u32`.
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In the ["Syntax" section](../01_intro/01_syntax.md) `compute`'s input parameters were of type `u32`.\
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Let's unpack what that _means_.
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Let's unpack what that _means_.
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## Primitive types
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## Primitive types
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### Signed vs. unsigned
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### Signed vs. unsigned
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|
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An integer can be **signed** or **unsigned**.
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An integer can be **signed** or **unsigned**.\
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An unsigned integer can only represent non-negative numbers (i.e. `0` or greater).
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An unsigned integer can only represent non-negative numbers (i.e. `0` or greater).
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A signed integer can represent both positive and negative numbers (e.g. `-1`, `12`, etc.).
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A signed integer can represent both positive and negative numbers (e.g. `-1`, `12`, etc.).
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The `u` in `u32` stands for **unsigned**.
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The `u` in `u32` stands for **unsigned**.\
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The equivalent type for signed integer is `i32`, where the `i` stands for integer (i.e. any integer, positive or
|
The equivalent type for signed integer is `i32`, where the `i` stands for integer (i.e. any integer, positive or
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negative).
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negative).
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### Bit width
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### Bit width
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The `32` in `u32` refers to the **number of bits[^bit]** used to represent the number in memory.
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The `32` in `u32` refers to the **number of bits[^bit]** used to represent the number in memory.\
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The more bits, the larger the range of numbers that can be represented.
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The more bits, the larger the range of numbers that can be represented.
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Rust supports multiple bit widths for integers: `8`, `16`, `32`, `64`, `128`.
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Rust supports multiple bit widths for integers: `8`, `16`, `32`, `64`, `128`.
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|
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With 32 bits, `u32` can represent numbers from `0` to `2^32 - 1` (a.k.a. [`u32::MAX`](https://doc.rust-lang.org/std/primitive.u32.html#associatedconstant.MAX)).
|
With 32 bits, `u32` can represent numbers from `0` to `2^32 - 1` (a.k.a. [`u32::MAX`](https://doc.rust-lang.org/std/primitive.u32.html#associatedconstant.MAX)).\
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With the same number of bits, a signed integer (`i32`) can represent numbers from `-2^31` to `2^31 - 1`
|
With the same number of bits, a signed integer (`i32`) can represent numbers from `-2^31` to `2^31 - 1`
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(i.e. from [`i32::MIN`](https://doc.rust-lang.org/std/primitive.i32.html#associatedconstant.MIN)
|
(i.e. from [`i32::MIN`](https://doc.rust-lang.org/std/primitive.i32.html#associatedconstant.MIN)
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to [`i32::MAX`](https://doc.rust-lang.org/std/primitive.i32.html#associatedconstant.MAX)).
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to [`i32::MAX`](https://doc.rust-lang.org/std/primitive.i32.html#associatedconstant.MAX)).\
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The maximum value for `i32` is smaller than the maximum value for `u32` because one bit is used to represent
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The maximum value for `i32` is smaller than the maximum value for `u32` because one bit is used to represent
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the sign of the number. Check out the [two's complement](https://en.wikipedia.org/wiki/Two%27s_complement)
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the sign of the number. Check out the [two's complement](https://en.wikipedia.org/wiki/Two%27s_complement)
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representation for more details on how signed integers are represented in memory.
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representation for more details on how signed integers are represented in memory.
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@ -46,7 +46,7 @@ representation for more details on how signed integers are represented in memory
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Combining the two variables (signed/unsigned and bit width), we get the following integer types:
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Combining the two variables (signed/unsigned and bit width), we get the following integer types:
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|
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| Bit width | Signed | Unsigned |
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| Bit width | Signed | Unsigned |
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|-----------|--------|----------|
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| --------- | ------ | -------- |
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| 8-bit | `i8` | `u8` |
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| 8-bit | `i8` | `u8` |
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| 16-bit | `i16` | `u16` |
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| 16-bit | `i16` | `u16` |
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| 32-bit | `i32` | `u32` |
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| 32-bit | `i32` | `u32` |
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@ -55,21 +55,21 @@ Combining the two variables (signed/unsigned and bit width), we get the followin
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|
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## Literals
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## Literals
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|
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A **literal** is a notation for representing a fixed value in source code.
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A **literal** is a notation for representing a fixed value in source code.\
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For example, `42` is a Rust literal for the number forty-two.
|
For example, `42` is a Rust literal for the number forty-two.
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|
|
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### Type annotations for literals
|
### Type annotations for literals
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||||||
|
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But all values in Rust have a type, so... what's the type of `42`?
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But all values in Rust have a type, so... what's the type of `42`?
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|
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The Rust compiler will try to infer the type of a literal based on how it's used.
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The Rust compiler will try to infer the type of a literal based on how it's used.\
|
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If you don't provide any context, the compiler will default to `i32` for integer literals.
|
If you don't provide any context, the compiler will default to `i32` for integer literals.\
|
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If you want to use a different type, you can add the desired integer type as a suffix—e.g. `2u64` is a 2 that's
|
If you want to use a different type, you can add the desired integer type as a suffix—e.g. `2u64` is a 2 that's
|
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explicitly typed as a `u64`.
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explicitly typed as a `u64`.
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|
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### Underscores in literals
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### Underscores in literals
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|
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You can use underscores `_` to improve the readability of large numbers.
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You can use underscores `_` to improve the readability of large numbers.\
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For example, `1_000_000` is the same as `1000000`.
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For example, `1_000_000` is the same as `1000000`.
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|
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## Arithmetic operators
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## Arithmetic operators
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@ -82,7 +82,7 @@ Rust supports the following arithmetic operators[^traits] for integers:
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- `/` for division
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- `/` for division
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- `%` for remainder
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- `%` for remainder
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|
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Precedence and associativity rules for these operators are the same as in mathematics.
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Precedence and associativity rules for these operators are the same as in mathematics.\
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You can use parentheses to override the default precedence. E.g. `2 * (3 + 4)`.
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You can use parentheses to override the default precedence. E.g. `2 * (3 + 4)`.
|
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|
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> ⚠️ **Warning**
|
> ⚠️ **Warning**
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||||||
|
@ -92,7 +92,7 @@ You can use parentheses to override the default precedence. E.g. `2 * (3 + 4)`.
|
||||||
|
|
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## No automatic type coercion
|
## No automatic type coercion
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||||||
|
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As we discussed in the previous exercise, Rust is a statically typed language.
|
As we discussed in the previous exercise, Rust is a statically typed language.\
|
||||||
In particular, Rust is quite strict about type coercion. It won't automatically convert a value from one type to
|
In particular, Rust is quite strict about type coercion. It won't automatically convert a value from one type to
|
||||||
another[^coercion],
|
another[^coercion],
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||||||
even if the conversion is lossless. You have to do it explicitly.
|
even if the conversion is lossless. You have to do it explicitly.
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|
|
|
@ -1,6 +1,6 @@
|
||||||
# Variables
|
# Variables
|
||||||
|
|
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In Rust, you can use the `let` keyword to declare **variables**.
|
In Rust, you can use the `let` keyword to declare **variables**.\
|
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For example:
|
For example:
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||||||
|
|
||||||
```rust
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```rust
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||||||
|
@ -35,20 +35,20 @@ let x = 42;
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let y: u32 = x;
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let y: u32 = x;
|
||||||
```
|
```
|
||||||
|
|
||||||
In the example above, we didn't specify the type of `x`.
|
In the example above, we didn't specify the type of `x`.\
|
||||||
`x` is later assigned to `y`, which is explicitly typed as `u32`. Since Rust doesn't perform automatic type coercion,
|
`x` is later assigned to `y`, which is explicitly typed as `u32`. Since Rust doesn't perform automatic type coercion,
|
||||||
the compiler infers the type of `x` to be `u32`—the same as `y` and the only type that will allow the program to compile
|
the compiler infers the type of `x` to be `u32`—the same as `y` and the only type that will allow the program to compile
|
||||||
without errors.
|
without errors.
|
||||||
|
|
||||||
### Inference limitations
|
### Inference limitations
|
||||||
|
|
||||||
The compiler sometimes needs a little help to infer the correct variable type based on its usage.
|
The compiler sometimes needs a little help to infer the correct variable type based on its usage.\
|
||||||
In those cases you'll get a compilation error and the compiler will ask you to provide an explicit type hint to
|
In those cases you'll get a compilation error and the compiler will ask you to provide an explicit type hint to
|
||||||
disambiguate the situation.
|
disambiguate the situation.
|
||||||
|
|
||||||
## Function arguments are variables
|
## Function arguments are variables
|
||||||
|
|
||||||
Not all heroes wear capes, not all variables are declared with `let`.
|
Not all heroes wear capes, not all variables are declared with `let`.\
|
||||||
Function arguments are variables too!
|
Function arguments are variables too!
|
||||||
|
|
||||||
```rust
|
```rust
|
||||||
|
@ -57,22 +57,22 @@ fn add_one(x: u32) -> u32 {
|
||||||
}
|
}
|
||||||
```
|
```
|
||||||
|
|
||||||
In the example above, `x` is a variable of type `u32`.
|
In the example above, `x` is a variable of type `u32`.\
|
||||||
The only difference between `x` and a variable declared with `let` is that functions arguments **must** have their type
|
The only difference between `x` and a variable declared with `let` is that functions arguments **must** have their type
|
||||||
explicitly declared. The compiler won't infer it for you.
|
explicitly declared. The compiler won't infer it for you.\
|
||||||
This constraint allows the Rust compiler (and us humans!) to understand the function's signature without having to look
|
This constraint allows the Rust compiler (and us humans!) to understand the function's signature without having to look
|
||||||
at its implementation. That's a big boost for compilation speed[^speed]!
|
at its implementation. That's a big boost for compilation speed[^speed]!
|
||||||
|
|
||||||
## Initialization
|
## Initialization
|
||||||
|
|
||||||
You don't have to initialize a variable when you declare it.
|
You don't have to initialize a variable when you declare it.\
|
||||||
For example
|
For example
|
||||||
|
|
||||||
```rust
|
```rust
|
||||||
let x: u32;
|
let x: u32;
|
||||||
```
|
```
|
||||||
|
|
||||||
is a valid variable declaration.
|
is a valid variable declaration.\
|
||||||
However, you must initialize the variable before using it. The compiler will throw an error if you don't:
|
However, you must initialize the variable before using it. The compiler will throw an error if you don't:
|
||||||
|
|
||||||
```rust
|
```rust
|
||||||
|
|
|
@ -1,6 +1,6 @@
|
||||||
# Control flow, part 1
|
# Control flow, part 1
|
||||||
|
|
||||||
All our programs so far have been pretty straightforward.
|
All our programs so far have been pretty straightforward.\
|
||||||
A sequence of instructions is executed from top to bottom, and that's it.
|
A sequence of instructions is executed from top to bottom, and that's it.
|
||||||
|
|
||||||
It's time to introduce some **branching**.
|
It's time to introduce some **branching**.
|
||||||
|
@ -23,7 +23,7 @@ This program will print `number is smaller than 5` because the condition `number
|
||||||
### `else` clauses
|
### `else` clauses
|
||||||
|
|
||||||
Like most programming languages, Rust supports an optional `else` branch to execute a block of code when the condition in an
|
Like most programming languages, Rust supports an optional `else` branch to execute a block of code when the condition in an
|
||||||
`if` expression is false.
|
`if` expression is false.\
|
||||||
For example:
|
For example:
|
||||||
|
|
||||||
```rust
|
```rust
|
||||||
|
@ -38,7 +38,7 @@ if number < 5 {
|
||||||
|
|
||||||
## Booleans
|
## Booleans
|
||||||
|
|
||||||
The condition in an `if` expression must be of type `bool`, a **boolean**.
|
The condition in an `if` expression must be of type `bool`, a **boolean**.\
|
||||||
Booleans, just like integers, are a primitive type in Rust.
|
Booleans, just like integers, are a primitive type in Rust.
|
||||||
|
|
||||||
A boolean can have one of two values: `true` or `false`.
|
A boolean can have one of two values: `true` or `false`.
|
||||||
|
@ -67,12 +67,12 @@ error[E0308]: mismatched types
|
||||||
```
|
```
|
||||||
|
|
||||||
This follows from Rust's philosophy around type coercion: there's no automatic conversion from non-boolean types to booleans.
|
This follows from Rust's philosophy around type coercion: there's no automatic conversion from non-boolean types to booleans.
|
||||||
Rust doesn't have the concept of **truthy** or **falsy** values, like JavaScript or Python.
|
Rust doesn't have the concept of **truthy** or **falsy** values, like JavaScript or Python.\
|
||||||
You have to be explicit about the condition you want to check.
|
You have to be explicit about the condition you want to check.
|
||||||
|
|
||||||
### Comparison operators
|
### Comparison operators
|
||||||
|
|
||||||
It's quite common to use comparison operators to build conditions for `if` expressions.
|
It's quite common to use comparison operators to build conditions for `if` expressions.\
|
||||||
Here are the comparison operators available in Rust when working with integers:
|
Here are the comparison operators available in Rust when working with integers:
|
||||||
|
|
||||||
- `==`: equal to
|
- `==`: equal to
|
||||||
|
@ -84,7 +84,7 @@ Here are the comparison operators available in Rust when working with integers:
|
||||||
|
|
||||||
## `if/else` is an expression
|
## `if/else` is an expression
|
||||||
|
|
||||||
In Rust, `if` expressions are **expressions**, not statements: they return a value.
|
In Rust, `if` expressions are **expressions**, not statements: they return a value.\
|
||||||
That value can be assigned to a variable or used in other expressions. For example:
|
That value can be assigned to a variable or used in other expressions. For example:
|
||||||
|
|
||||||
```rust
|
```rust
|
||||||
|
@ -97,10 +97,9 @@ let message = if number < 5 {
|
||||||
```
|
```
|
||||||
|
|
||||||
In the example above, each branch of the `if` evaluates to a string literal,
|
In the example above, each branch of the `if` evaluates to a string literal,
|
||||||
which is then assigned to the `message` variable.
|
which is then assigned to the `message` variable.\
|
||||||
The only requirement is that both `if` branches return the same type.
|
The only requirement is that both `if` branches return the same type.
|
||||||
|
|
||||||
|
|
||||||
## References
|
## References
|
||||||
|
|
||||||
- The exercise for this section is located in `exercises/02_basic_calculator/03_if_else`
|
- The exercise for this section is located in `exercises/02_basic_calculator/03_if_else`
|
|
@ -13,7 +13,7 @@ fn speed(start: u32, end: u32, time_elapsed: u32) -> u32 {
|
||||||
If you have a keen eye, you might have spotted one issue[^one]: what happens if `time_elapsed` is zero?
|
If you have a keen eye, you might have spotted one issue[^one]: what happens if `time_elapsed` is zero?
|
||||||
|
|
||||||
You can try it
|
You can try it
|
||||||
out [on the Rust playground](https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=36e5ddbe3b3f741dfa9f74c956622bac)!
|
out [on the Rust playground](https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=36e5ddbe3b3f741dfa9f74c956622bac)!\
|
||||||
The program will exit with the following error message:
|
The program will exit with the following error message:
|
||||||
|
|
||||||
```text
|
```text
|
||||||
|
@ -21,7 +21,7 @@ thread 'main' panicked at src/main.rs:3:5:
|
||||||
attempt to divide by zero
|
attempt to divide by zero
|
||||||
```
|
```
|
||||||
|
|
||||||
This is known as a **panic**.
|
This is known as a **panic**.\
|
||||||
A panic is Rust's way to signal that something went so wrong that
|
A panic is Rust's way to signal that something went so wrong that
|
||||||
the program can't continue executing, it's an **unrecoverable error**[^catching]. Division by zero classifies as such an
|
the program can't continue executing, it's an **unrecoverable error**[^catching]. Division by zero classifies as such an
|
||||||
error.
|
error.
|
||||||
|
|
|
@ -1,6 +1,6 @@
|
||||||
# Loops, part 1: `while`
|
# Loops, part 1: `while`
|
||||||
|
|
||||||
Your implementation of `factorial` has been forced to use recursion.
|
Your implementation of `factorial` has been forced to use recursion.\
|
||||||
This may feel natural to you, especially if you're coming from a functional programming background.
|
This may feel natural to you, especially if you're coming from a functional programming background.
|
||||||
Or it may feel strange, if you're used to more imperative languages like C or Python.
|
Or it may feel strange, if you're used to more imperative languages like C or Python.
|
||||||
|
|
||||||
|
@ -8,7 +8,7 @@ Let's see how you can implement the same functionality using a **loop** instead.
|
||||||
|
|
||||||
## The `while` loop
|
## The `while` loop
|
||||||
|
|
||||||
A `while` loop is a way to execute a block of code as long as a **condition** is true.
|
A `while` loop is a way to execute a block of code as long as a **condition** is true.\
|
||||||
Here's the general syntax:
|
Here's the general syntax:
|
||||||
|
|
||||||
```rust
|
```rust
|
||||||
|
@ -62,7 +62,7 @@ error[E0384]: cannot assign twice to immutable variable `i`
|
||||||
| ^^^^^^ cannot assign twice to immutable variable
|
| ^^^^^^ cannot assign twice to immutable variable
|
||||||
```
|
```
|
||||||
|
|
||||||
This is because variables in Rust are **immutable** by default.
|
This is because variables in Rust are **immutable** by default.\
|
||||||
You can't change their value once it has been assigned.
|
You can't change their value once it has been assigned.
|
||||||
|
|
||||||
If you want to allow modifications, you have to declare the variable as **mutable** using the `mut` keyword:
|
If you want to allow modifications, you have to declare the variable as **mutable** using the `mut` keyword:
|
||||||
|
|
|
@ -1,6 +1,6 @@
|
||||||
# Loops, part 2: `for`
|
# Loops, part 2: `for`
|
||||||
|
|
||||||
Having to manually increment a counter variable is somewhat tedious. The pattern is also extremely common!
|
Having to manually increment a counter variable is somewhat tedious. The pattern is also extremely common!\
|
||||||
To make this easier, Rust provides a more concise way to iterate over a range of values: the `for` loop.
|
To make this easier, Rust provides a more concise way to iterate over a range of values: the `for` loop.
|
||||||
|
|
||||||
## The `for` loop
|
## The `for` loop
|
||||||
|
|
|
@ -1,18 +1,18 @@
|
||||||
# Overflow
|
# Overflow
|
||||||
|
|
||||||
The factorial of a number grows quite fast.
|
The factorial of a number grows quite fast.\
|
||||||
For example, the factorial of 20 is 2,432,902,008,176,640,000. That's already bigger than the maximum value for a
|
For example, the factorial of 20 is 2,432,902,008,176,640,000. That's already bigger than the maximum value for a
|
||||||
32-bit integer, 2,147,483,647.
|
32-bit integer, 2,147,483,647.
|
||||||
|
|
||||||
When the result of an arithmetic operation is bigger than the maximum value for a given integer type,
|
When the result of an arithmetic operation is bigger than the maximum value for a given integer type,
|
||||||
we are talking about **an integer overflow**.
|
we are talking about **an integer overflow**.
|
||||||
|
|
||||||
Integer overflows are an issue because they violate the contract for arithmetic operations.
|
Integer overflows are an issue because they violate the contract for arithmetic operations.\
|
||||||
The result of an arithmetic operation between two integers of a given type should be another integer of the same type.
|
The result of an arithmetic operation between two integers of a given type should be another integer of the same type.
|
||||||
But the _mathematically correct result_ doesn't fit into that integer type!
|
But the _mathematically correct result_ doesn't fit into that integer type!
|
||||||
|
|
||||||
> If the result is smaller than the minimum value for a given integer type, we refer to the event as **an integer
|
> If the result is smaller than the minimum value for a given integer type, we refer to the event as **an integer
|
||||||
> underflow**.
|
> underflow**.\
|
||||||
> For brevity, we'll only talk about integer overflows for the rest of this section, but keep in mind that
|
> For brevity, we'll only talk about integer overflows for the rest of this section, but keep in mind that
|
||||||
> everything we say applies to integer underflows as well.
|
> everything we say applies to integer underflows as well.
|
||||||
>
|
>
|
||||||
|
@ -32,7 +32,7 @@ is not Rust's solution to the integer overflow problem.
|
||||||
|
|
||||||
## Alternatives
|
## Alternatives
|
||||||
|
|
||||||
Since we ruled out automatic promotion, what can we do when an integer overflow occurs?
|
Since we ruled out automatic promotion, what can we do when an integer overflow occurs?\
|
||||||
It boils down to two different approaches:
|
It boils down to two different approaches:
|
||||||
|
|
||||||
- Reject the operation
|
- Reject the operation
|
||||||
|
@ -40,13 +40,13 @@ It boils down to two different approaches:
|
||||||
|
|
||||||
### Reject the operation
|
### Reject the operation
|
||||||
|
|
||||||
This is the most conservative approach: we stop the program when an integer overflow occurs.
|
This is the most conservative approach: we stop the program when an integer overflow occurs.\
|
||||||
That's done via a panic, the mechanism we've already seen in the ["Panics" section](04_panics.md).
|
That's done via a panic, the mechanism we've already seen in the ["Panics" section](04_panics.md).
|
||||||
|
|
||||||
### Come up with a "sensible" result
|
### Come up with a "sensible" result
|
||||||
|
|
||||||
When the result of an arithmetic operation is bigger than the maximum value for a given integer type, you can
|
When the result of an arithmetic operation is bigger than the maximum value for a given integer type, you can
|
||||||
choose to **wrap around**.
|
choose to **wrap around**.\
|
||||||
If you think of all the possible values for a given integer type as a circle, wrapping around means that when you
|
If you think of all the possible values for a given integer type as a circle, wrapping around means that when you
|
||||||
reach the maximum value, you start again from the minimum value.
|
reach the maximum value, you start again from the minimum value.
|
||||||
|
|
||||||
|
@ -69,14 +69,14 @@ You may be wondering—what is a profile setting? Let's get into that!
|
||||||
A [**profile**](https://doc.rust-lang.org/cargo/reference/profiles.html) is a set of configuration options that can be
|
A [**profile**](https://doc.rust-lang.org/cargo/reference/profiles.html) is a set of configuration options that can be
|
||||||
used to customize the way Rust code is compiled.
|
used to customize the way Rust code is compiled.
|
||||||
|
|
||||||
Cargo provides two built-in profiles: `dev` and `release`.
|
Cargo provides two built-in profiles: `dev` and `release`.\
|
||||||
The `dev` profile is used every time you run `cargo build`, `cargo run` or `cargo test`. It's aimed at local
|
The `dev` profile is used every time you run `cargo build`, `cargo run` or `cargo test`. It's aimed at local
|
||||||
development,
|
development,
|
||||||
therefore it sacrifices runtime performance in favor of faster compilation times and a better debugging experience.
|
therefore it sacrifices runtime performance in favor of faster compilation times and a better debugging experience.\
|
||||||
The `release` profile, instead, is optimized for runtime performance but incurs longer compilation times. You need
|
The `release` profile, instead, is optimized for runtime performance but incurs longer compilation times. You need
|
||||||
to explicitly request via the `--release` flag—e.g. `cargo build --release` or `cargo run --release`.
|
to explicitly request via the `--release` flag—e.g. `cargo build --release` or `cargo run --release`.
|
||||||
|
|
||||||
> "Have you built your project in release mode?" is almost a meme in the Rust community.
|
> "Have you built your project in release mode?" is almost a meme in the Rust community.\
|
||||||
> It refers to developers who are not familiar with Rust and complain about its performance on
|
> It refers to developers who are not familiar with Rust and complain about its performance on
|
||||||
> social media (e.g. Reddit, Twitter, etc.) before realizing they haven't built their project in
|
> social media (e.g. Reddit, Twitter, etc.) before realizing they haven't built their project in
|
||||||
> release mode.
|
> release mode.
|
||||||
|
@ -90,12 +90,12 @@ By default, `overflow-checks` is set to:
|
||||||
- `true` for the `dev` profile
|
- `true` for the `dev` profile
|
||||||
- `false` for the `release` profile
|
- `false` for the `release` profile
|
||||||
|
|
||||||
This is in line with the goals of the two profiles.
|
This is in line with the goals of the two profiles.\
|
||||||
`dev` is aimed at local development, so it panics in order to highlight potential issues as early as possible.
|
`dev` is aimed at local development, so it panics in order to highlight potential issues as early as possible.\
|
||||||
`release`, instead, is tuned for runtime performance: checking for overflows would slow down the program, so it
|
`release`, instead, is tuned for runtime performance: checking for overflows would slow down the program, so it
|
||||||
prefers to wrap around.
|
prefers to wrap around.
|
||||||
|
|
||||||
At the same time, having different behaviours for the two profiles can lead to subtle bugs.
|
At the same time, having different behaviours for the two profiles can lead to subtle bugs.\
|
||||||
Our recommendation is to enable `overflow-checks` for both profiles: it's better to crash than to silently produce
|
Our recommendation is to enable `overflow-checks` for both profiles: it's better to crash than to silently produce
|
||||||
incorrect results. The runtime performance hit is negligible in most cases; if you're working on a performance-critical
|
incorrect results. The runtime performance hit is negligible in most cases; if you're working on a performance-critical
|
||||||
application, you can run benchmarks to decide if it's something you can afford.
|
application, you can run benchmarks to decide if it's something you can afford.
|
||||||
|
|
|
@ -1,12 +1,12 @@
|
||||||
# Case-by-case behavior
|
# Case-by-case behavior
|
||||||
|
|
||||||
`overflow-checks` is a blunt tool: it's a global setting that affects the whole program.
|
`overflow-checks` is a blunt tool: it's a global setting that affects the whole program.\
|
||||||
It often happens that you want to handle integer overflows differently depending on the context: sometimes
|
It often happens that you want to handle integer overflows differently depending on the context: sometimes
|
||||||
wrapping is the right choice, other times panicking is preferable.
|
wrapping is the right choice, other times panicking is preferable.
|
||||||
|
|
||||||
## `wrapping_` methods
|
## `wrapping_` methods
|
||||||
|
|
||||||
You can opt into wrapping arithmetic on a per-operation basis by using the `wrapping_` methods[^method].
|
You can opt into wrapping arithmetic on a per-operation basis by using the `wrapping_` methods[^method].\
|
||||||
For example, you can use `wrapping_add` to add two integers with wrapping:
|
For example, you can use `wrapping_add` to add two integers with wrapping:
|
||||||
|
|
||||||
```rust
|
```rust
|
||||||
|
@ -18,7 +18,7 @@ assert_eq!(sum, 0);
|
||||||
|
|
||||||
## `saturating_` methods
|
## `saturating_` methods
|
||||||
|
|
||||||
Alternatively, you can opt into **saturating arithmetic** by using the `saturating_` methods.
|
Alternatively, you can opt into **saturating arithmetic** by using the `saturating_` methods.\
|
||||||
Instead of wrapping around, saturating arithmetic will return the maximum or minimum value for the integer type.
|
Instead of wrapping around, saturating arithmetic will return the maximum or minimum value for the integer type.
|
||||||
For example:
|
For example:
|
||||||
|
|
||||||
|
@ -29,7 +29,7 @@ let sum = x.saturating_add(y);
|
||||||
assert_eq!(sum, 255);
|
assert_eq!(sum, 255);
|
||||||
```
|
```
|
||||||
|
|
||||||
Since `255 + 1` is `256`, which is bigger than `u8::MAX`, the result is `u8::MAX` (255).
|
Since `255 + 1` is `256`, which is bigger than `u8::MAX`, the result is `u8::MAX` (255).\
|
||||||
The opposite happens for underflows: `0 - 1` is `-1`, which is smaller than `u8::MIN`, so the result is `u8::MIN` (0).
|
The opposite happens for underflows: `0 - 1` is `-1`, which is smaller than `u8::MIN`, so the result is `u8::MIN` (0).
|
||||||
|
|
||||||
You can't get saturating arithmetic via the `overflow-checks` profile setting—you have to explicitly opt into it
|
You can't get saturating arithmetic via the `overflow-checks` profile setting—you have to explicitly opt into it
|
||||||
|
|
|
@ -1,12 +1,12 @@
|
||||||
# Conversions, pt. 1
|
# Conversions, pt. 1
|
||||||
|
|
||||||
We've repeated over and over again that Rust won't perform
|
We've repeated over and over again that Rust won't perform
|
||||||
implicit type conversions for integers.
|
implicit type conversions for integers.\
|
||||||
How do you perform _explicit_ conversions then?
|
How do you perform _explicit_ conversions then?
|
||||||
|
|
||||||
## `as`
|
## `as`
|
||||||
|
|
||||||
You can use the `as` operator to convert between integer types.
|
You can use the `as` operator to convert between integer types.\
|
||||||
`as` conversions are **infallible**.
|
`as` conversions are **infallible**.
|
||||||
|
|
||||||
For example:
|
For example:
|
||||||
|
@ -62,7 +62,7 @@ memory representation:
|
||||||
Last 8 bits
|
Last 8 bits
|
||||||
```
|
```
|
||||||
|
|
||||||
Hence `256 as u8` is equal to `0`. That's... not ideal, in most scenarios.
|
Hence `256 as u8` is equal to `0`. That's... not ideal, in most scenarios.\
|
||||||
In fact, the Rust compiler will actively try to stop you if it sees you trying
|
In fact, the Rust compiler will actively try to stop you if it sees you trying
|
||||||
to cast a literal value which will result in a truncation:
|
to cast a literal value which will result in a truncation:
|
||||||
|
|
||||||
|
@ -79,17 +79,17 @@ error: literal out of range for `i8`
|
||||||
|
|
||||||
### Recommendation
|
### Recommendation
|
||||||
|
|
||||||
As a rule of thumb, be quite careful with `as` casting.
|
As a rule of thumb, be quite careful with `as` casting.\
|
||||||
Use it _exclusively_ for going from a smaller type to a larger type.
|
Use it _exclusively_ for going from a smaller type to a larger type.
|
||||||
To convert from a larger to smaller integer type, rely on the
|
To convert from a larger to smaller integer type, rely on the
|
||||||
[*fallible* conversion machinery](../05_ticket_v2/13_try_from.md) that we'll
|
[_fallible_ conversion machinery](../05_ticket_v2/13_try_from.md) that we'll
|
||||||
explore later in the course.
|
explore later in the course.
|
||||||
|
|
||||||
### Limitations
|
### Limitations
|
||||||
|
|
||||||
Surprising behaviour is not the only downside of `as` casting.
|
Surprising behaviour is not the only downside of `as` casting.
|
||||||
It is also fairly limited: you can only rely on `as` casting
|
It is also fairly limited: you can only rely on `as` casting
|
||||||
for primitive types and a few other special cases.
|
for primitive types and a few other special cases.\
|
||||||
When working with composite types, you'll have to rely on
|
When working with composite types, you'll have to rely on
|
||||||
different conversion mechanisms ([fallible](../05_ticket_v2/13_try_from.md)
|
different conversion mechanisms ([fallible](../05_ticket_v2/13_try_from.md)
|
||||||
and [infallible](../04_traits/09_from.md)), which we'll explore later on.
|
and [infallible](../04_traits/09_from.md)), which we'll explore later on.
|
||||||
|
|
|
@ -1,14 +1,14 @@
|
||||||
# Modelling A Ticket
|
# Modelling A Ticket
|
||||||
|
|
||||||
The first chapter should have given you a good grasp over some of Rust's primitive types, operators and
|
The first chapter should have given you a good grasp over some of Rust's primitive types, operators and
|
||||||
basic control flow constructs.
|
basic control flow constructs.\
|
||||||
In this chapter we'll go one step further and cover what makes Rust truly unique: **ownership**.
|
In this chapter we'll go one step further and cover what makes Rust truly unique: **ownership**.\
|
||||||
Ownership is what enables Rust to be both memory-safe and performant, with no garbage collector.
|
Ownership is what enables Rust to be both memory-safe and performant, with no garbage collector.
|
||||||
|
|
||||||
As our running example, we'll use a (JIRA-like) ticket, the kind you'd use to track bugs, features, or tasks in
|
As our running example, we'll use a (JIRA-like) ticket, the kind you'd use to track bugs, features, or tasks in
|
||||||
a software project.
|
a software project.\
|
||||||
We'll take a stab at modeling it in Rust. It'll be the first iteration—it won't be perfect nor very idiomatic
|
We'll take a stab at modeling it in Rust. It'll be the first iteration—it won't be perfect nor very idiomatic
|
||||||
by the end of the chapter. It'll be enough of a challenge though!
|
by the end of the chapter. It'll be enough of a challenge though!\
|
||||||
To move forward you'll have to pick up several new Rust concepts, such as:
|
To move forward you'll have to pick up several new Rust concepts, such as:
|
||||||
|
|
||||||
- `struct`s, one of Rust's ways to define custom types
|
- `struct`s, one of Rust's ways to define custom types
|
||||||
|
|
|
@ -28,7 +28,7 @@ A struct is quite similar to what you would call a class or an object in other p
|
||||||
|
|
||||||
## Defining fields
|
## Defining fields
|
||||||
|
|
||||||
The new type is built by combining other types as **fields**.
|
The new type is built by combining other types as **fields**.\
|
||||||
Each field must have a name and a type, separated by a colon, `:`. If there are multiple fields, they are separated by a comma, `,`.
|
Each field must have a name and a type, separated by a colon, `:`. If there are multiple fields, they are separated by a comma, `,`.
|
||||||
|
|
||||||
Fields don't have to be of the same type, as you can see in the `Configuration` struct below:
|
Fields don't have to be of the same type, as you can see in the `Configuration` struct below:
|
||||||
|
@ -64,7 +64,7 @@ let x = ticket.description;
|
||||||
|
|
||||||
## Methods
|
## Methods
|
||||||
|
|
||||||
We can attach behaviour to our structs by defining **methods**.
|
We can attach behaviour to our structs by defining **methods**.\
|
||||||
Using the `Ticket` struct as an example:
|
Using the `Ticket` struct as an example:
|
||||||
|
|
||||||
```rust
|
```rust
|
||||||
|
@ -140,4 +140,3 @@ but it's definitely more verbose. Prefer the method call syntax when possible.
|
||||||
## References
|
## References
|
||||||
|
|
||||||
- The exercise for this section is located in `exercises/03_ticket_v1/01_struct`
|
- The exercise for this section is located in `exercises/03_ticket_v1/01_struct`
|
||||||
|
|
|
@ -12,7 +12,7 @@ struct Ticket {
|
||||||
|
|
||||||
We are using "raw" types for the fields of our `Ticket` struct.
|
We are using "raw" types for the fields of our `Ticket` struct.
|
||||||
This means that users can create a ticket with an empty title, a suuuuuuuper long description or
|
This means that users can create a ticket with an empty title, a suuuuuuuper long description or
|
||||||
a nonsensical status (e.g. "Funny").
|
a nonsensical status (e.g. "Funny").\
|
||||||
We can do better than that!
|
We can do better than that!
|
||||||
|
|
||||||
## References
|
## References
|
||||||
|
|
|
@ -9,7 +9,7 @@ Let's start with modules.
|
||||||
|
|
||||||
## What is a module?
|
## What is a module?
|
||||||
|
|
||||||
In Rust a **module** is a way to group related code together, under a common namespace (i.e. the module's name).
|
In Rust a **module** is a way to group related code together, under a common namespace (i.e. the module's name).\
|
||||||
You've already seen modules in action: the unit tests that verify the correctness of your code are defined in a
|
You've already seen modules in action: the unit tests that verify the correctness of your code are defined in a
|
||||||
different module, named `tests`.
|
different module, named `tests`.
|
||||||
|
|
||||||
|
@ -27,7 +27,7 @@ contents (the stuff inside `{ ... }`) are next to each other.
|
||||||
|
|
||||||
## Module tree
|
## Module tree
|
||||||
|
|
||||||
Modules can be nested, forming a **tree** structure.
|
Modules can be nested, forming a **tree** structure.\
|
||||||
The root of the tree is the **crate** itself, which is the top-level module that contains all the other modules.
|
The root of the tree is the **crate** itself, which is the top-level module that contains all the other modules.
|
||||||
For a library crate, the root module is usually `src/lib.rs` (unless its location has been customized).
|
For a library crate, the root module is usually `src/lib.rs` (unless its location has been customized).
|
||||||
The root module is also known as the **crate root**.
|
The root module is also known as the **crate root**.
|
||||||
|
@ -44,7 +44,7 @@ mod dog;
|
||||||
```
|
```
|
||||||
|
|
||||||
`cargo`, Rust's build tool, is then in charge of finding the file that contains
|
`cargo`, Rust's build tool, is then in charge of finding the file that contains
|
||||||
the module implementation.
|
the module implementation.\
|
||||||
If your module is declared in the root of your crate (e.g. `src/lib.rs` or `src/main.rs`),
|
If your module is declared in the root of your crate (e.g. `src/lib.rs` or `src/main.rs`),
|
||||||
`cargo` expects the file to be named either:
|
`cargo` expects the file to be named either:
|
||||||
|
|
||||||
|
@ -76,7 +76,7 @@ fn mark_ticket_as_done(ticket: Ticket) {
|
||||||
}
|
}
|
||||||
```
|
```
|
||||||
|
|
||||||
That's not the case if you want to access an entity from a different module.
|
That's not the case if you want to access an entity from a different module.\
|
||||||
You have to use a **path** pointing to the entity you want to access.
|
You have to use a **path** pointing to the entity you want to access.
|
||||||
|
|
||||||
You can compose the path in various ways:
|
You can compose the path in various ways:
|
||||||
|
@ -106,9 +106,9 @@ You can also import all the items from a module with a single `use` statement.
|
||||||
use crate::module_1::module_2::*;
|
use crate::module_1::module_2::*;
|
||||||
```
|
```
|
||||||
|
|
||||||
This is known as a **star import**.
|
This is known as a **star import**.\
|
||||||
It is generally discouraged because it can pollute the current namespace, making it hard to understand
|
It is generally discouraged because it can pollute the current namespace, making it hard to understand
|
||||||
where each name comes from and potentially introducing name conflicts.
|
where each name comes from and potentially introducing name conflicts.\
|
||||||
Nonetheless, it can be useful in some cases, like when writing unit tests. You might have noticed
|
Nonetheless, it can be useful in some cases, like when writing unit tests. You might have noticed
|
||||||
that most of our test modules start with a `use super::*;` statement to bring all the items from the parent module
|
that most of our test modules start with a `use super::*;` statement to bring all the items from the parent module
|
||||||
(the one being tested) into scope.
|
(the one being tested) into scope.
|
||||||
|
|
|
@ -6,7 +6,7 @@ be it a struct, a function, a field, etc.
|
||||||
|
|
||||||
## Private by default
|
## Private by default
|
||||||
|
|
||||||
By default, everything in Rust is **private**.
|
By default, everything in Rust is **private**.\
|
||||||
A private entity can only be accessed:
|
A private entity can only be accessed:
|
||||||
|
|
||||||
1. within the same module where it's defined, or
|
1. within the same module where it's defined, or
|
||||||
|
@ -22,7 +22,7 @@ We've used this extensively in the previous exercises:
|
||||||
|
|
||||||
## Visibility modifiers
|
## Visibility modifiers
|
||||||
|
|
||||||
You can modify the default visibility of an entity using a **visibility modifier**.
|
You can modify the default visibility of an entity using a **visibility modifier**.\
|
||||||
Some common visibility modifiers are:
|
Some common visibility modifiers are:
|
||||||
|
|
||||||
- `pub`: makes the entity **public**, i.e. accessible from outside the module where it's defined, potentially from
|
- `pub`: makes the entity **public**, i.e. accessible from outside the module where it's defined, potentially from
|
||||||
|
|
|
@ -1,6 +1,6 @@
|
||||||
# Encapsulation
|
# Encapsulation
|
||||||
|
|
||||||
Now that we have a basic understanding of modules and visibility, let's circle back to **encapsulation**.
|
Now that we have a basic understanding of modules and visibility, let's circle back to **encapsulation**.\
|
||||||
Encapsulation is the practice of hiding the internal representation of an object. It is most commonly
|
Encapsulation is the practice of hiding the internal representation of an object. It is most commonly
|
||||||
used to enforce some **invariants** on the object's state.
|
used to enforce some **invariants** on the object's state.
|
||||||
|
|
||||||
|
@ -14,7 +14,7 @@ struct Ticket {
|
||||||
}
|
}
|
||||||
```
|
```
|
||||||
|
|
||||||
If all fields are made public, there is no encapsulation.
|
If all fields are made public, there is no encapsulation.\
|
||||||
You must assume that the fields can be modified at any time, set to any value that's allowed by
|
You must assume that the fields can be modified at any time, set to any value that's allowed by
|
||||||
their type. You can't rule out that a ticket might have an empty title or a status
|
their type. You can't rule out that a ticket might have an empty title or a status
|
||||||
that doesn't make sense.
|
that doesn't make sense.
|
||||||
|
@ -35,9 +35,9 @@ let ticket = Ticket {
|
||||||
};
|
};
|
||||||
```
|
```
|
||||||
|
|
||||||
You've seen this in action in the previous exercise on visibility.
|
You've seen this in action in the previous exercise on visibility.\
|
||||||
We now need to provide one or more public **constructors**—i.e. static methods or functions that can be used
|
We now need to provide one or more public **constructors**—i.e. static methods or functions that can be used
|
||||||
from outside the module to create a new instance of the struct.
|
from outside the module to create a new instance of the struct.\
|
||||||
Luckily enough we already have one: `Ticket::new`, as implemented in [a previous exercise](02_validation.md).
|
Luckily enough we already have one: `Ticket::new`, as implemented in [a previous exercise](02_validation.md).
|
||||||
|
|
||||||
## Accessor methods
|
## Accessor methods
|
||||||
|
@ -50,7 +50,7 @@ In summary:
|
||||||
That's a good start, but it's not enough: apart from creating a `Ticket`, we also need to interact with it.
|
That's a good start, but it's not enough: apart from creating a `Ticket`, we also need to interact with it.
|
||||||
But how can we access the fields if they're private?
|
But how can we access the fields if they're private?
|
||||||
|
|
||||||
We need to provide **accessor methods**.
|
We need to provide **accessor methods**.\
|
||||||
Accessor methods are public methods that allow you to read the value of a private field (or fields) of a struct.
|
Accessor methods are public methods that allow you to read the value of a private field (or fields) of a struct.
|
||||||
|
|
||||||
Rust doesn't have a built-in way to generate accessor methods for you, like some other languages do.
|
Rust doesn't have a built-in way to generate accessor methods for you, like some other languages do.
|
||||||
|
|
|
@ -74,11 +74,11 @@ All these things are true at the same time for Rust:
|
||||||
2. As a developer, you rarely have to manage memory directly
|
2. As a developer, you rarely have to manage memory directly
|
||||||
3. You can't cause dangling pointers, double frees, and other memory-related bugs
|
3. You can't cause dangling pointers, double frees, and other memory-related bugs
|
||||||
|
|
||||||
Languages like Python, JavaScript, and Java give you 2. and 3., but not 1.
|
Languages like Python, JavaScript, and Java give you 2. and 3., but not 1.\
|
||||||
Language like C or C++ give you 1., but neither 2. nor 3.
|
Language like C or C++ give you 1., but neither 2. nor 3.
|
||||||
|
|
||||||
Depending on your background, 3. might sound a bit arcane: what is a "dangling pointer"?
|
Depending on your background, 3. might sound a bit arcane: what is a "dangling pointer"?
|
||||||
What is a "double free"? Why are they dangerous?
|
What is a "double free"? Why are they dangerous?\
|
||||||
Don't worry: we'll cover these concepts in more details during the rest of the course.
|
Don't worry: we'll cover these concepts in more details during the rest of the course.
|
||||||
|
|
||||||
For now, though, let's focus on learning how to work within Rust's ownership system.
|
For now, though, let's focus on learning how to work within Rust's ownership system.
|
||||||
|
@ -113,7 +113,7 @@ impl Ticket {
|
||||||
}
|
}
|
||||||
```
|
```
|
||||||
|
|
||||||
`Ticket::description` takes ownership of the `Ticket` instance it's called on.
|
`Ticket::description` takes ownership of the `Ticket` instance it's called on.\
|
||||||
This is known as **move semantics**: ownership of the value (`self`) is **moved** from the caller to
|
This is known as **move semantics**: ownership of the value (`self`) is **moved** from the caller to
|
||||||
the callee, and the caller can't use it anymore.
|
the callee, and the caller can't use it anymore.
|
||||||
|
|
||||||
|
@ -152,10 +152,10 @@ To build _useful_ accessor methods we need to start working with **references**.
|
||||||
|
|
||||||
## Borrowing
|
## Borrowing
|
||||||
|
|
||||||
It is desirable to have methods that can read the value of a variable without taking ownership of it.
|
It is desirable to have methods that can read the value of a variable without taking ownership of it.\
|
||||||
Programming would be quite limited otherwise. In Rust, that's done via **borrowing**.
|
Programming would be quite limited otherwise. In Rust, that's done via **borrowing**.
|
||||||
|
|
||||||
Whenever you borrow a value, you get a **reference** to it.
|
Whenever you borrow a value, you get a **reference** to it.\
|
||||||
References are tagged with their privileges[^refine]:
|
References are tagged with their privileges[^refine]:
|
||||||
|
|
||||||
- Immutable references (`&`) allow you to read the value, but not to mutate it
|
- Immutable references (`&`) allow you to read the value, but not to mutate it
|
||||||
|
@ -180,7 +180,7 @@ All these restrictions are enforced at compile-time by the borrow checker.
|
||||||
|
|
||||||
### Syntax
|
### Syntax
|
||||||
|
|
||||||
How do you borrow a value, in practice?
|
How do you borrow a value, in practice?\
|
||||||
By adding `&` or `&mut` **in front a variable**, you're borrowing its value.
|
By adding `&` or `&mut` **in front a variable**, you're borrowing its value.
|
||||||
Careful though! The same symbols (`&` and `&mut`) in **front of a type** have a different meaning:
|
Careful though! The same symbols (`&` and `&mut`) in **front of a type** have a different meaning:
|
||||||
they denote a different type, a reference to the original type.
|
they denote a different type, a reference to the original type.
|
||||||
|
@ -220,14 +220,14 @@ fn f(number: &mut u32) -> &u32 {
|
||||||
|
|
||||||
## Breathe in, breathe out
|
## Breathe in, breathe out
|
||||||
|
|
||||||
Rust's ownership system can be a bit overwhelming at first.
|
Rust's ownership system can be a bit overwhelming at first.\
|
||||||
But don't worry: it'll become second nature with practice.
|
But don't worry: it'll become second nature with practice.\
|
||||||
And you're going to get a lot of practice over the rest of this chapter, as well as the rest of the course!
|
And you're going to get a lot of practice over the rest of this chapter, as well as the rest of the course!
|
||||||
We'll revisit each concept multiple times to make sure you get familiar with them
|
We'll revisit each concept multiple times to make sure you get familiar with them
|
||||||
and truly understand how they work.
|
and truly understand how they work.
|
||||||
|
|
||||||
Towards the end of this chapter we'll explain *why* Rust's ownership system is designed the way it is.
|
Towards the end of this chapter we'll explain _why_ Rust's ownership system is designed the way it is.
|
||||||
For the time being, focus on understanding the *how*. Take each compiler error as a learning opportunity!
|
For the time being, focus on understanding the _how_. Take each compiler error as a learning opportunity!
|
||||||
|
|
||||||
## References
|
## References
|
||||||
|
|
||||||
|
|
|
@ -18,7 +18,7 @@ impl Ticket {
|
||||||
}
|
}
|
||||||
```
|
```
|
||||||
|
|
||||||
A sprinkle of `&` here and there did the trick!
|
A sprinkle of `&` here and there did the trick!\
|
||||||
We now have a way to access the fields of a `Ticket` instance without consuming it in the process.
|
We now have a way to access the fields of a `Ticket` instance without consuming it in the process.
|
||||||
Let's see how we can enhance our `Ticket` struct with **setter methods** next.
|
Let's see how we can enhance our `Ticket` struct with **setter methods** next.
|
||||||
|
|
||||||
|
@ -46,7 +46,7 @@ impl Ticket {
|
||||||
}
|
}
|
||||||
```
|
```
|
||||||
|
|
||||||
It takes ownership of `self`, changes the title, and returns the modified `Ticket` instance.
|
It takes ownership of `self`, changes the title, and returns the modified `Ticket` instance.\
|
||||||
This is how you'd use it:
|
This is how you'd use it:
|
||||||
|
|
||||||
```rust
|
```rust
|
||||||
|
|
|
@ -5,16 +5,16 @@ Now it's a good time to take a look under the hood: let's talk about **memory**.
|
||||||
|
|
||||||
## Stack and heap
|
## Stack and heap
|
||||||
|
|
||||||
When discussing memory, you'll often hear people talk about the **stack** and the **heap**.
|
When discussing memory, you'll often hear people talk about the **stack** and the **heap**.\
|
||||||
These are two different memory regions used by programs to store data.
|
These are two different memory regions used by programs to store data.
|
||||||
|
|
||||||
Let's start with the stack.
|
Let's start with the stack.
|
||||||
|
|
||||||
## Stack
|
## Stack
|
||||||
|
|
||||||
The **stack** is a **LIFO** (Last In, First Out) data structure.
|
The **stack** is a **LIFO** (Last In, First Out) data structure.\
|
||||||
When you call a function, a new **stack frame** is added on top of the stack. That stack frame stores
|
When you call a function, a new **stack frame** is added on top of the stack. That stack frame stores
|
||||||
the function's arguments, local variables and a few "bookkeeping" values.
|
the function's arguments, local variables and a few "bookkeeping" values.\
|
||||||
When the function returns, the stack frame is popped off the stack[^stack-overflow].
|
When the function returns, the stack frame is popped off the stack[^stack-overflow].
|
||||||
|
|
||||||
```text
|
```text
|
||||||
|
@ -25,15 +25,15 @@ When the function returns, the stack frame is popped off the stack[^stack-overfl
|
||||||
+-----------------+ +-----------------+ +-----------------+
|
+-----------------+ +-----------------+ +-----------------+
|
||||||
```
|
```
|
||||||
|
|
||||||
From an operational point of view, stack allocation/de-allocation is **very fast**.
|
From an operational point of view, stack allocation/de-allocation is **very fast**.\
|
||||||
We are always pushing and popping data from the top of the stack, so we don't need to search for free memory.
|
We are always pushing and popping data from the top of the stack, so we don't need to search for free memory.
|
||||||
We also don't have to worry about fragmentation: the stack is a single contiguous block of memory.
|
We also don't have to worry about fragmentation: the stack is a single contiguous block of memory.
|
||||||
|
|
||||||
### Rust
|
### Rust
|
||||||
|
|
||||||
Rust will often allocate data on the stack.
|
Rust will often allocate data on the stack.\
|
||||||
You have a `u32` input argument in a function? Those 32 bits will be on the stack.
|
You have a `u32` input argument in a function? Those 32 bits will be on the stack.\
|
||||||
You define a local variable of type `i64`? Those 64 bits will be on the stack.
|
You define a local variable of type `i64`? Those 64 bits will be on the stack.\
|
||||||
It all works quite nicely because the size of those integers is known at compile time, therefore
|
It all works quite nicely because the size of those integers is known at compile time, therefore
|
||||||
the compiled program knows how much space it needs to reserve on the stack for them.
|
the compiled program knows how much space it needs to reserve on the stack for them.
|
||||||
|
|
||||||
|
|
|
@ -6,14 +6,14 @@ That's where the **heap** comes in.
|
||||||
|
|
||||||
## Heap allocations
|
## Heap allocations
|
||||||
|
|
||||||
You can visualize the heap as a big chunk of memory—a huge array, if you will.
|
You can visualize the heap as a big chunk of memory—a huge array, if you will.\
|
||||||
Whenever you need to store data on the heap, you ask a special program, the **allocator**, to reserve for you
|
Whenever you need to store data on the heap, you ask a special program, the **allocator**, to reserve for you
|
||||||
a subset of the heap. We call this interaction (and the memory you reserved) a **heap allocation**.
|
a subset of the heap. We call this interaction (and the memory you reserved) a **heap allocation**.
|
||||||
If the allocation succeeds, the allocator will give you a **pointer** to the start of the reserved block.
|
If the allocation succeeds, the allocator will give you a **pointer** to the start of the reserved block.
|
||||||
|
|
||||||
## No automatic de-allocation
|
## No automatic de-allocation
|
||||||
|
|
||||||
The heap is structured quite differently from the stack.
|
The heap is structured quite differently from the stack.\
|
||||||
Heap allocations are not contiguous, they can be located anywhere inside the heap.
|
Heap allocations are not contiguous, they can be located anywhere inside the heap.
|
||||||
|
|
||||||
```
|
```
|
||||||
|
@ -29,7 +29,7 @@ calling the allocator again to **free** the memory you no longer need.
|
||||||
## Performance
|
## Performance
|
||||||
|
|
||||||
The heap's flexibility comes at a cost: heap allocations are **slower** than stack allocations.
|
The heap's flexibility comes at a cost: heap allocations are **slower** than stack allocations.
|
||||||
There's a lot more bookkeeping involved!
|
There's a lot more bookkeeping involved!\
|
||||||
If you read articles about performance optimization you'll often be advised to minimize heap allocations
|
If you read articles about performance optimization you'll often be advised to minimize heap allocations
|
||||||
and prefer stack-allocated data whenever possible.
|
and prefer stack-allocated data whenever possible.
|
||||||
|
|
||||||
|
@ -37,7 +37,7 @@ and prefer stack-allocated data whenever possible.
|
||||||
|
|
||||||
When you create a local variable of type `String`,
|
When you create a local variable of type `String`,
|
||||||
Rust is forced to allocate on the heap[^empty]: it doesn't know in advance how much text you're going to put in it,
|
Rust is forced to allocate on the heap[^empty]: it doesn't know in advance how much text you're going to put in it,
|
||||||
so it can't reserve the right amount of space on the stack.
|
so it can't reserve the right amount of space on the stack.\
|
||||||
But a `String` is not _entirely_ heap-allocated, it also keeps some data on the stack. In particular:
|
But a `String` is not _entirely_ heap-allocated, it also keeps some data on the stack. In particular:
|
||||||
|
|
||||||
- The **pointer** to the heap region you reserved.
|
- The **pointer** to the heap region you reserved.
|
||||||
|
@ -65,9 +65,9 @@ Heap: | ? | ? | ? | ? | ? |
|
||||||
+---+---+---+---+---+
|
+---+---+---+---+---+
|
||||||
```
|
```
|
||||||
|
|
||||||
We asked for a `String` that can hold up to 5 bytes of text.
|
We asked for a `String` that can hold up to 5 bytes of text.\
|
||||||
`String::with_capacity` goes to the allocator and asks for 5 bytes of heap memory. The allocator returns
|
`String::with_capacity` goes to the allocator and asks for 5 bytes of heap memory. The allocator returns
|
||||||
a pointer to the start of that memory block.
|
a pointer to the start of that memory block.\
|
||||||
The `String` is empty, though. On the stack, we keep track of this information by distinguishing between
|
The `String` is empty, though. On the stack, we keep track of this information by distinguishing between
|
||||||
the length and the capacity: this `String` can hold up to 5 bytes, but it currently holds 0 bytes of
|
the length and the capacity: this `String` can hold up to 5 bytes, but it currently holds 0 bytes of
|
||||||
actual text.
|
actual text.
|
||||||
|
@ -96,7 +96,7 @@ Three of the five bytes on the heap are used to store the characters `H`, `e`, a
|
||||||
|
|
||||||
### `usize`
|
### `usize`
|
||||||
|
|
||||||
How much space do we need to store pointer, length and capacity on the stack?
|
How much space do we need to store pointer, length and capacity on the stack?\
|
||||||
It depends on the **architecture** of the machine you're running on.
|
It depends on the **architecture** of the machine you're running on.
|
||||||
|
|
||||||
Every memory location on your machine has an [**address**](https://en.wikipedia.org/wiki/Memory_address), commonly
|
Every memory location on your machine has an [**address**](https://en.wikipedia.org/wiki/Memory_address), commonly
|
||||||
|
@ -118,7 +118,7 @@ which is also known as the **size of the type**.
|
||||||
> What about the memory buffer that `String` is managing on the heap? Isn't that
|
> What about the memory buffer that `String` is managing on the heap? Isn't that
|
||||||
> part of the size of `String`?
|
> part of the size of `String`?
|
||||||
|
|
||||||
No!
|
No!\
|
||||||
That heap allocation is a **resource** that `String` is managing.
|
That heap allocation is a **resource** that `String` is managing.
|
||||||
It's not considered to be part of the `String` type by the compiler.
|
It's not considered to be part of the `String` type by the compiler.
|
||||||
|
|
||||||
|
@ -129,7 +129,7 @@ therefore it doesn't track its size.
|
||||||
Unfortunately there is no equivalent of `std::mem::size_of` to measure the amount of
|
Unfortunately there is no equivalent of `std::mem::size_of` to measure the amount of
|
||||||
heap memory that a certain value is allocating at runtime. Some types might
|
heap memory that a certain value is allocating at runtime. Some types might
|
||||||
provide methods to inspect their heap usage (e.g. `String`'s `capacity` method),
|
provide methods to inspect their heap usage (e.g. `String`'s `capacity` method),
|
||||||
but there is no general-purpose "API" to retrieve runtime heap usage in Rust.
|
but there is no general-purpose "API" to retrieve runtime heap usage in Rust.\
|
||||||
You can, however, use a memory profiler tool (e.g. [DHAT](https://valgrind.org/docs/manual/dh-manual.html)
|
You can, however, use a memory profiler tool (e.g. [DHAT](https://valgrind.org/docs/manual/dh-manual.html)
|
||||||
or [a custom allocator](https://docs.rs/dhat/latest/dhat/)) to inspect the heap usage of your program.
|
or [a custom allocator](https://docs.rs/dhat/latest/dhat/)) to inspect the heap usage of your program.
|
||||||
|
|
||||||
|
|
|
@ -2,7 +2,7 @@
|
||||||
|
|
||||||
What about references, like `&String` or `&mut String`? How are they represented in memory?
|
What about references, like `&String` or `&mut String`? How are they represented in memory?
|
||||||
|
|
||||||
Most references[^fat] in Rust are represented, in memory, as a pointer to a memory location.
|
Most references[^fat] in Rust are represented, in memory, as a pointer to a memory location.\
|
||||||
It follows that their size is the same as the size of a pointer, a `usize`.
|
It follows that their size is the same as the size of a pointer, a `usize`.
|
||||||
|
|
||||||
You can verify this using `std::mem::size_of`:
|
You can verify this using `std::mem::size_of`:
|
||||||
|
@ -12,7 +12,7 @@ assert_eq!(std::mem::size_of::<&String>(), 8);
|
||||||
assert_eq!(std::mem::size_of::<&mut String>(), 8);
|
assert_eq!(std::mem::size_of::<&mut String>(), 8);
|
||||||
```
|
```
|
||||||
|
|
||||||
A `&String`, in particular, is a pointer to the memory location where the `String`'s metadata is stored.
|
A `&String`, in particular, is a pointer to the memory location where the `String`'s metadata is stored.\
|
||||||
If you run this snippet:
|
If you run this snippet:
|
||||||
|
|
||||||
```rust
|
```rust
|
||||||
|
@ -42,7 +42,7 @@ The same goes for `&mut String`.
|
||||||
|
|
||||||
## Not all pointers point to the heap
|
## Not all pointers point to the heap
|
||||||
|
|
||||||
The example above should clarify one thing: not all pointers point to the heap.
|
The example above should clarify one thing: not all pointers point to the heap.\
|
||||||
They just point to a memory location, which _may_ be on the heap, but doesn't have to be.
|
They just point to a memory location, which _may_ be on the heap, but doesn't have to be.
|
||||||
|
|
||||||
## References
|
## References
|
||||||
|
|
|
@ -1,6 +1,6 @@
|
||||||
# Destructors
|
# Destructors
|
||||||
|
|
||||||
When introducing the heap, we mentioned that you're responsible for freeing the memory you allocate.
|
When introducing the heap, we mentioned that you're responsible for freeing the memory you allocate.\
|
||||||
When introducing the borrow-checker, we also stated that you rarely have to manage memory directly in Rust.
|
When introducing the borrow-checker, we also stated that you rarely have to manage memory directly in Rust.
|
||||||
|
|
||||||
These two statements might seem contradictory at first.
|
These two statements might seem contradictory at first.
|
||||||
|
@ -38,10 +38,10 @@ It ends when one of the following happens:
|
||||||
|
|
||||||
## Destructors
|
## Destructors
|
||||||
|
|
||||||
When the owner of a value goes out of scope, Rust invokes its **destructor**.
|
When the owner of a value goes out of scope, Rust invokes its **destructor**.\
|
||||||
The destructor tries to clean up the resources used by that value—in particular, whatever memory it allocated.
|
The destructor tries to clean up the resources used by that value—in particular, whatever memory it allocated.
|
||||||
|
|
||||||
You can manually invoke the destructor of a value by passing it to `std::mem::drop`.
|
You can manually invoke the destructor of a value by passing it to `std::mem::drop`.\
|
||||||
That's why you'll often hear Rust developers saying "that value has been **dropped**" as a way to state that a value
|
That's why you'll often hear Rust developers saying "that value has been **dropped**" as a way to state that a value
|
||||||
has gone out of scope and its destructor has been invoked.
|
has gone out of scope and its destructor has been invoked.
|
||||||
|
|
||||||
|
@ -129,12 +129,12 @@ error[E0382]: use of moved value: `x`
|
||||||
| ^ value used here after move
|
| ^ value used here after move
|
||||||
```
|
```
|
||||||
|
|
||||||
Drop **consumes** the value it's called on, meaning that the value is no longer valid after the call.
|
Drop **consumes** the value it's called on, meaning that the value is no longer valid after the call.\
|
||||||
The compiler will therefore prevent you from using it, avoiding [use-after-free bugs](https://owasp.org/www-community/vulnerabilities/Using_freed_memory).
|
The compiler will therefore prevent you from using it, avoiding [use-after-free bugs](https://owasp.org/www-community/vulnerabilities/Using_freed_memory).
|
||||||
|
|
||||||
### Dropping references
|
### Dropping references
|
||||||
|
|
||||||
What if a variable contains a reference?
|
What if a variable contains a reference?\
|
||||||
For example:
|
For example:
|
||||||
|
|
||||||
```rust
|
```rust
|
||||||
|
@ -143,7 +143,7 @@ let y = &x;
|
||||||
drop(y);
|
drop(y);
|
||||||
```
|
```
|
||||||
|
|
||||||
When you call `drop(y)`... nothing happens.
|
When you call `drop(y)`... nothing happens.\
|
||||||
If you actually try to compile this code, you'll get a warning:
|
If you actually try to compile this code, you'll get a warning:
|
||||||
|
|
||||||
```text
|
```text
|
||||||
|
@ -158,7 +158,7 @@ warning: calls to `std::mem::drop` with a reference
|
||||||
|
|
|
|
||||||
```
|
```
|
||||||
|
|
||||||
It goes back to what we said earlier: we only want to call the destructor once.
|
It goes back to what we said earlier: we only want to call the destructor once.\
|
||||||
You can have multiple references to the same value—if we called the destructor for the value they point at
|
You can have multiple references to the same value—if we called the destructor for the value they point at
|
||||||
when one of them goes out of scope, what would happen to the others?
|
when one of them goes out of scope, what would happen to the others?
|
||||||
They would refer to a memory location that's no longer valid: a so-called [**dangling pointer**](https://en.wikipedia.org/wiki/Dangling_pointer),
|
They would refer to a memory location that's no longer valid: a so-called [**dangling pointer**](https://en.wikipedia.org/wiki/Dangling_pointer),
|
||||||
|
|
|
@ -1,6 +1,6 @@
|
||||||
# Wrapping up
|
# Wrapping up
|
||||||
|
|
||||||
We've covered a lot of foundational Rust concepts in this chapter.
|
We've covered a lot of foundational Rust concepts in this chapter.\
|
||||||
Before moving on, let's go through one last exercise to consolidate what we've learned.
|
Before moving on, let's go through one last exercise to consolidate what we've learned.
|
||||||
You'll have minimal guidance this time—just the exercise description and the tests to guide you.
|
You'll have minimal guidance this time—just the exercise description and the tests to guide you.
|
||||||
|
|
||||||
|
|
|
@ -1,9 +1,9 @@
|
||||||
# Traits
|
# Traits
|
||||||
|
|
||||||
In the previous chapter we covered the basics of Rust's type and ownership system.
|
In the previous chapter we covered the basics of Rust's type and ownership system.\
|
||||||
It's time to dig deeper: we'll explore **traits**, Rust's take on interfaces.
|
It's time to dig deeper: we'll explore **traits**, Rust's take on interfaces.
|
||||||
|
|
||||||
Once you learn about traits, you'll start seeing their fingerprints all over the place.
|
Once you learn about traits, you'll start seeing their fingerprints all over the place.\
|
||||||
In fact, you've already seen traits in action throughout the previous chapter, e.g. `.into()` invocations as well
|
In fact, you've already seen traits in action throughout the previous chapter, e.g. `.into()` invocations as well
|
||||||
as operators like `==` and `+`.
|
as operators like `==` and `+`.
|
||||||
|
|
||||||
|
|
|
@ -38,7 +38,7 @@ error[E0369]: binary operation `==` cannot be applied to type `Ticket`
|
||||||
note: an implementation of `PartialEq` might be missing for `Ticket`
|
note: an implementation of `PartialEq` might be missing for `Ticket`
|
||||||
```
|
```
|
||||||
|
|
||||||
`Ticket` is a new type. Out of the box, there is **no behavior attached to it**.
|
`Ticket` is a new type. Out of the box, there is **no behavior attached to it**.\
|
||||||
Rust doesn't magically infer how to compare two `Ticket` instances just because they contain `String`s.
|
Rust doesn't magically infer how to compare two `Ticket` instances just because they contain `String`s.
|
||||||
|
|
||||||
The Rust compiler is nudging us in the right direction though: it's suggesting that we might be missing an implementation
|
The Rust compiler is nudging us in the right direction though: it's suggesting that we might be missing an implementation
|
||||||
|
@ -46,7 +46,7 @@ of `PartialEq`. `PartialEq` is a **trait**!
|
||||||
|
|
||||||
## What are traits?
|
## What are traits?
|
||||||
|
|
||||||
Traits are Rust's way of defining **interfaces**.
|
Traits are Rust's way of defining **interfaces**.\
|
||||||
A trait defines a set of methods that a type must implement to satisfy the trait's contract.
|
A trait defines a set of methods that a type must implement to satisfy the trait's contract.
|
||||||
|
|
||||||
### Defining a trait
|
### Defining a trait
|
||||||
|
|
|
@ -44,7 +44,7 @@ fn main() {
|
||||||
|
|
||||||
## One implementation
|
## One implementation
|
||||||
|
|
||||||
There are limitations to the trait implementations you can write.
|
There are limitations to the trait implementations you can write.\
|
||||||
The simplest and most straight-forward one: you can't implement the same trait twice,
|
The simplest and most straight-forward one: you can't implement the same trait twice,
|
||||||
in a crate, for the same type.
|
in a crate, for the same type.
|
||||||
|
|
||||||
|
@ -101,7 +101,7 @@ Imagine the following situation:
|
||||||
- Crate `C` provides a (different) implementation of the `IsEven` trait for `u32`
|
- Crate `C` provides a (different) implementation of the `IsEven` trait for `u32`
|
||||||
- Crate `D` depends on both `B` and `C` and calls `1.is_even()`
|
- Crate `D` depends on both `B` and `C` and calls `1.is_even()`
|
||||||
|
|
||||||
Which implementation should be used? The one defined in `B`? Or the one defined in `C`?
|
Which implementation should be used? The one defined in `B`? Or the one defined in `C`?\
|
||||||
There's no good answer, therefore the orphan rule was defined to prevent this scenario.
|
There's no good answer, therefore the orphan rule was defined to prevent this scenario.
|
||||||
Thanks to the orphan rule, neither crate `B` nor crate `C` would compile.
|
Thanks to the orphan rule, neither crate `B` nor crate `C` would compile.
|
||||||
|
|
||||||
|
|
|
@ -5,7 +5,7 @@ Operator overloading is the ability to define custom behavior for operators like
|
||||||
|
|
||||||
## Operators are traits
|
## Operators are traits
|
||||||
|
|
||||||
In Rust, operators are traits.
|
In Rust, operators are traits.\
|
||||||
For each operator, there is a corresponding trait that defines the behavior of that operator.
|
For each operator, there is a corresponding trait that defines the behavior of that operator.
|
||||||
By implementing that trait for your type, you **unlock** the usage of the corresponding operators.
|
By implementing that trait for your type, you **unlock** the usage of the corresponding operators.
|
||||||
|
|
||||||
|
@ -33,7 +33,7 @@ and replace `x == y` with `x.eq(y)`. It's syntactic sugar!
|
||||||
This is the correspondence for the main operators:
|
This is the correspondence for the main operators:
|
||||||
|
|
||||||
| Operator | Trait |
|
| Operator | Trait |
|
||||||
|--------------------------|-------------------------------------------------------------------------|
|
| ------------------------ | ----------------------------------------------------------------------- |
|
||||||
| `+` | [`Add`](https://doc.rust-lang.org/std/ops/trait.Add.html) |
|
| `+` | [`Add`](https://doc.rust-lang.org/std/ops/trait.Add.html) |
|
||||||
| `-` | [`Sub`](https://doc.rust-lang.org/std/ops/trait.Sub.html) |
|
| `-` | [`Sub`](https://doc.rust-lang.org/std/ops/trait.Sub.html) |
|
||||||
| `*` | [`Mul`](https://doc.rust-lang.org/std/ops/trait.Mul.html) |
|
| `*` | [`Mul`](https://doc.rust-lang.org/std/ops/trait.Mul.html) |
|
||||||
|
@ -47,9 +47,9 @@ while comparison ones live in the [`std::cmp`](https://doc.rust-lang.org/std/cmp
|
||||||
|
|
||||||
## Default implementations
|
## Default implementations
|
||||||
|
|
||||||
The comment on `PartialEq::ne` states that "`ne` is a provided method".
|
The comment on `PartialEq::ne` states that "`ne` is a provided method".\
|
||||||
It means that `PartialEq` provides a **default implementation** for `ne` in the trait definition—the `{ ... }` elided
|
It means that `PartialEq` provides a **default implementation** for `ne` in the trait definition—the `{ ... }` elided
|
||||||
block in the definition snippet.
|
block in the definition snippet.\
|
||||||
If we expand the elided block, it looks like this:
|
If we expand the elided block, it looks like this:
|
||||||
|
|
||||||
```rust
|
```rust
|
||||||
|
@ -62,7 +62,7 @@ pub trait PartialEq {
|
||||||
}
|
}
|
||||||
```
|
```
|
||||||
|
|
||||||
It's what you expect: `ne` is the negation of `eq`.
|
It's what you expect: `ne` is the negation of `eq`.\
|
||||||
Since a default implementation is provided, you can skip implementing `ne` when you implement `PartialEq` for your type.
|
Since a default implementation is provided, you can skip implementing `ne` when you implement `PartialEq` for your type.
|
||||||
It's enough to implement `eq`:
|
It's enough to implement `eq`:
|
||||||
|
|
||||||
|
|
|
@ -24,7 +24,7 @@ impl PartialEq for Ticket {
|
||||||
```
|
```
|
||||||
|
|
||||||
If the definition of `Ticket` changes, the compiler will error out, complaining that your
|
If the definition of `Ticket` changes, the compiler will error out, complaining that your
|
||||||
destructuring is no longer exhaustive.
|
destructuring is no longer exhaustive.\
|
||||||
You can also rename struct fields, to avoid variable shadowing:
|
You can also rename struct fields, to avoid variable shadowing:
|
||||||
|
|
||||||
```rust
|
```rust
|
||||||
|
@ -55,7 +55,7 @@ You've already encountered a few macros in past exercises:
|
||||||
- `assert_eq!` and `assert!`, in the test cases
|
- `assert_eq!` and `assert!`, in the test cases
|
||||||
- `println!`, to print to the console
|
- `println!`, to print to the console
|
||||||
|
|
||||||
Rust macros are **code generators**.
|
Rust macros are **code generators**.\
|
||||||
They generate new Rust code based on the input you provide, and that generated code is then compiled alongside
|
They generate new Rust code based on the input you provide, and that generated code is then compiled alongside
|
||||||
the rest of your program. Some macros are built into Rust's standard library, but you can also
|
the rest of your program. Some macros are built into Rust's standard library, but you can also
|
||||||
write your own. We won't be creating our macro in this course, but you can find some useful
|
write your own. We won't be creating our macro in this course, but you can find some useful
|
||||||
|
|
|
@ -9,9 +9,9 @@ There's a third use case: **generic programming**.
|
||||||
|
|
||||||
## The problem
|
## The problem
|
||||||
|
|
||||||
All our functions and methods, so far, have been working with **concrete types**.
|
All our functions and methods, so far, have been working with **concrete types**.\
|
||||||
Code that operates on concrete types is usually straightforward to write and understand. But it's also
|
Code that operates on concrete types is usually straightforward to write and understand. But it's also
|
||||||
limited in its reusability.
|
limited in its reusability.\
|
||||||
Let's imagine, for example, that we want to write a function that returns `true` if an integer is even.
|
Let's imagine, for example, that we want to write a function that returns `true` if an integer is even.
|
||||||
Working with concrete types, we'd have to write a separate function for each integer type we want to
|
Working with concrete types, we'd have to write a separate function for each integer type we want to
|
||||||
support:
|
support:
|
||||||
|
@ -54,7 +54,7 @@ The duplication remains.
|
||||||
|
|
||||||
## Generic programming
|
## Generic programming
|
||||||
|
|
||||||
We can do better using **generics**.
|
We can do better using **generics**.\
|
||||||
Generics allow us to write code that works with a **type parameter** instead of a concrete type:
|
Generics allow us to write code that works with a **type parameter** instead of a concrete type:
|
||||||
|
|
||||||
```rust
|
```rust
|
||||||
|
@ -68,19 +68,19 @@ where
|
||||||
}
|
}
|
||||||
```
|
```
|
||||||
|
|
||||||
`print_if_even` is a **generic function**.
|
`print_if_even` is a **generic function**.\
|
||||||
It isn't tied to a specific input type. Instead, it works with any type `T` that:
|
It isn't tied to a specific input type. Instead, it works with any type `T` that:
|
||||||
|
|
||||||
- Implements the `IsEven` trait.
|
- Implements the `IsEven` trait.
|
||||||
- Implements the `Debug` trait.
|
- Implements the `Debug` trait.
|
||||||
|
|
||||||
This contract is expressed with a **trait bound**: `T: IsEven + Debug`.
|
This contract is expressed with a **trait bound**: `T: IsEven + Debug`.\
|
||||||
The `+` symbol is used to require that `T` implements multiple traits. `T: IsEven + Debug` is equivalent to
|
The `+` symbol is used to require that `T` implements multiple traits. `T: IsEven + Debug` is equivalent to
|
||||||
"where `T` implements `IsEven` **and** `Debug`".
|
"where `T` implements `IsEven` **and** `Debug`".
|
||||||
|
|
||||||
## Trait bounds
|
## Trait bounds
|
||||||
|
|
||||||
What purpose do trait bounds serve in `print_if_even`?
|
What purpose do trait bounds serve in `print_if_even`?\
|
||||||
To find out, let's try to remove them:
|
To find out, let's try to remove them:
|
||||||
|
|
||||||
```rust
|
```rust
|
||||||
|
@ -114,9 +114,9 @@ help: consider restricting type parameter `T`
|
||||||
| +++++++++++++++++
|
| +++++++++++++++++
|
||||||
```
|
```
|
||||||
|
|
||||||
Without trait bounds, the compiler doesn't know what `T` **can do**.
|
Without trait bounds, the compiler doesn't know what `T` **can do**.\
|
||||||
It doesn't know that `T` has an `is_even` method, and it doesn't know how to format `T` for printing.
|
It doesn't know that `T` has an `is_even` method, and it doesn't know how to format `T` for printing.
|
||||||
From the compiler point of view, a bare `T` has no behaviour at all.
|
From the compiler point of view, a bare `T` has no behaviour at all.\
|
||||||
Trait bounds restrict the set of types that can be used by ensuring that the behaviour required by the function
|
Trait bounds restrict the set of types that can be used by ensuring that the behaviour required by the function
|
||||||
body is present.
|
body is present.
|
||||||
|
|
||||||
|
@ -148,7 +148,7 @@ fn print_if_even<T: IsEven + Debug>(n: T) {
|
||||||
## Syntax: meaningful names
|
## Syntax: meaningful names
|
||||||
|
|
||||||
In the examples above, we used `T` as the type parameter name. This is a common convention when a function has
|
In the examples above, we used `T` as the type parameter name. This is a common convention when a function has
|
||||||
only one type parameter.
|
only one type parameter.\
|
||||||
Nothing stops you from using a more meaningful name, though:
|
Nothing stops you from using a more meaningful name, though:
|
||||||
|
|
||||||
```rust
|
```rust
|
||||||
|
@ -164,8 +164,8 @@ Follow Rust's conventions though: use camel case for type parameter names.
|
||||||
|
|
||||||
## The function signature is king
|
## The function signature is king
|
||||||
|
|
||||||
You may wonder why we need trait bounds at all. Can't the compiler infer the required traits from the function's body?
|
You may wonder why we need trait bounds at all. Can't the compiler infer the required traits from the function's body?\
|
||||||
It could, but it won't.
|
It could, but it won't.\
|
||||||
The rationale is the same as for [explicit type annotations on function parameters](../02_basic_calculator/02_variables.md#function-arguments-are-variables):
|
The rationale is the same as for [explicit type annotations on function parameters](../02_basic_calculator/02_variables.md#function-arguments-are-variables):
|
||||||
each function signature is a contract between the caller and the callee, and the terms must be explicitly stated.
|
each function signature is a contract between the caller and the callee, and the terms must be explicitly stated.
|
||||||
This allows for better error messages, better documentation, less unintentional breakages across versions,
|
This allows for better error messages, better documentation, less unintentional breakages across versions,
|
||||||
|
|
|
@ -16,7 +16,7 @@ The type of `s` is `&str`, a **reference to a string slice**.
|
||||||
|
|
||||||
## Memory layout
|
## Memory layout
|
||||||
|
|
||||||
`&str` and `String` are different types—they're not interchangeable.
|
`&str` and `String` are different types—they're not interchangeable.\
|
||||||
Let's recall the memory layout of a `String` from our
|
Let's recall the memory layout of a `String` from our
|
||||||
[previous exploration](../03_ticket_v1/09_heap.md).
|
[previous exploration](../03_ticket_v1/09_heap.md).
|
||||||
If we run:
|
If we run:
|
||||||
|
@ -59,7 +59,7 @@ how a `&String` is laid out in memory:
|
||||||
+---+---+---+---+---+
|
+---+---+---+---+---+
|
||||||
```
|
```
|
||||||
|
|
||||||
`&String` points to the memory location where the `String`'s metadata is stored.
|
`&String` points to the memory location where the `String`'s metadata is stored.\
|
||||||
If we follow the pointer, we get to the heap-allocated data. In particular, we get to the first byte of the string, `H`.
|
If we follow the pointer, we get to the heap-allocated data. In particular, we get to the first byte of the string, `H`.
|
||||||
|
|
||||||
What if we wanted a type that represents a **substring** of `s`? E.g. `ello` in `Hello`?
|
What if we wanted a type that represents a **substring** of `s`? E.g. `ello` in `Hello`?
|
||||||
|
@ -100,19 +100,19 @@ Heap: | H | e | l | l | o | |
|
||||||
- A pointer to the first byte of the slice.
|
- A pointer to the first byte of the slice.
|
||||||
- The length of the slice.
|
- The length of the slice.
|
||||||
|
|
||||||
`slice` doesn't own the data, it just points to it: it's a **reference** to the `String`'s heap-allocated data.
|
`slice` doesn't own the data, it just points to it: it's a **reference** to the `String`'s heap-allocated data.\
|
||||||
When `slice` is dropped, the heap-allocated data won't be deallocated, because it's still owned by `s`.
|
When `slice` is dropped, the heap-allocated data won't be deallocated, because it's still owned by `s`.
|
||||||
That's why `slice` doesn't have a `capacity` field: it doesn't own the data, so it doesn't need to know how much
|
That's why `slice` doesn't have a `capacity` field: it doesn't own the data, so it doesn't need to know how much
|
||||||
space it was allocated for it; it only cares about the data it references.
|
space it was allocated for it; it only cares about the data it references.
|
||||||
|
|
||||||
## `&str` vs `&String`
|
## `&str` vs `&String`
|
||||||
|
|
||||||
As a rule of thumb, use `&str` rather than `&String` whenever you need a reference to textual data.
|
As a rule of thumb, use `&str` rather than `&String` whenever you need a reference to textual data.\
|
||||||
`&str` is more flexible and generally considered more idiomatic in Rust code.
|
`&str` is more flexible and generally considered more idiomatic in Rust code.
|
||||||
|
|
||||||
If a method returns a `&String`, you're promising that there is heap-allocated UTF-8 text somewhere that
|
If a method returns a `&String`, you're promising that there is heap-allocated UTF-8 text somewhere that
|
||||||
**matches exactly** the one you're returning a reference to.
|
**matches exactly** the one you're returning a reference to.\
|
||||||
If a method returns a `&str`, instead, you have a lot more freedom: you're just saying that *somewhere* there's a
|
If a method returns a `&str`, instead, you have a lot more freedom: you're just saying that _somewhere_ there's a
|
||||||
bunch of text data and that a subset of it matches what you need, therefore you're returning a reference to it.
|
bunch of text data and that a subset of it matches what you need, therefore you're returning a reference to it.
|
||||||
|
|
||||||
## References
|
## References
|
||||||
|
|
|
@ -38,7 +38,7 @@ Instead, it just works. **Why**?
|
||||||
|
|
||||||
## `Deref` to the rescue
|
## `Deref` to the rescue
|
||||||
|
|
||||||
The `Deref` trait is the mechanism behind the language feature known as [**deref coercion**](https://doc.rust-lang.org/std/ops/trait.Deref.html#deref-coercion).
|
The `Deref` trait is the mechanism behind the language feature known as [**deref coercion**](https://doc.rust-lang.org/std/ops/trait.Deref.html#deref-coercion).\
|
||||||
The trait is defined in the standard library, in the `std::ops` module:
|
The trait is defined in the standard library, in the `std::ops` module:
|
||||||
|
|
||||||
```rust
|
```rust
|
||||||
|
@ -51,13 +51,13 @@ pub trait Deref {
|
||||||
}
|
}
|
||||||
```
|
```
|
||||||
|
|
||||||
`type Target` is an **associated type**.
|
`type Target` is an **associated type**.\
|
||||||
It's a placeholder for a concrete type that must be specified when the trait is implemented.
|
It's a placeholder for a concrete type that must be specified when the trait is implemented.
|
||||||
|
|
||||||
## Deref coercion
|
## Deref coercion
|
||||||
|
|
||||||
By implementing `Deref<Target = U>` for a type `T` you're telling the compiler that `&T` and `&U` are
|
By implementing `Deref<Target = U>` for a type `T` you're telling the compiler that `&T` and `&U` are
|
||||||
somewhat interchangeable.
|
somewhat interchangeable.\
|
||||||
In particular, you get the following behavior:
|
In particular, you get the following behavior:
|
||||||
|
|
||||||
- References to `T` are implicitly converted into references to `U` (i.e. `&T` becomes `&U`)
|
- References to `T` are implicitly converted into references to `U` (i.e. `&T` becomes `&U`)
|
||||||
|
@ -84,7 +84,7 @@ Thanks to this implementation and deref coercion, a `&String` is automatically c
|
||||||
|
|
||||||
## Don't abuse deref coercion
|
## Don't abuse deref coercion
|
||||||
|
|
||||||
Deref coercion is a powerful feature, but it can lead to confusion.
|
Deref coercion is a powerful feature, but it can lead to confusion.\
|
||||||
Automatically converting types can make the code harder to read and understand. If a method with the same name
|
Automatically converting types can make the code harder to read and understand. If a method with the same name
|
||||||
is defined on both `T` and `U`, which one will be called?
|
is defined on both `T` and `U`, which one will be called?
|
||||||
|
|
||||||
|
|
|
@ -1,7 +1,7 @@
|
||||||
# `Sized`
|
# `Sized`
|
||||||
|
|
||||||
There's more to `&str` than meets the eye, even after having
|
There's more to `&str` than meets the eye, even after having
|
||||||
investigated deref coercion.
|
investigated deref coercion.\
|
||||||
From our previous [discussion on memory layouts](../03_ticket_v1/10_references_in_memory.md),
|
From our previous [discussion on memory layouts](../03_ticket_v1/10_references_in_memory.md),
|
||||||
it would have been reasonable to expect `&str` to be represented as a single `usize` on
|
it would have been reasonable to expect `&str` to be represented as a single `usize` on
|
||||||
the stack, a pointer. That's not the case though. `&str` stores some **metadata** next
|
the stack, a pointer. That's not the case though. `&str` stores some **metadata** next
|
||||||
|
@ -38,10 +38,10 @@ What's going on?
|
||||||
|
|
||||||
## Dynamically sized types
|
## Dynamically sized types
|
||||||
|
|
||||||
`str` is a **dynamically sized type** (DST).
|
`str` is a **dynamically sized type** (DST).\
|
||||||
A DST is a type whose size is not known at compile time. Whenever you have a
|
A DST is a type whose size is not known at compile time. Whenever you have a
|
||||||
reference to a DST, like `&str`, it has to include additional
|
reference to a DST, like `&str`, it has to include additional
|
||||||
information about the data it points to. It is a **fat pointer**.
|
information about the data it points to. It is a **fat pointer**.\
|
||||||
In the case of `&str`, it stores the length of the slice it points to.
|
In the case of `&str`, it stores the length of the slice it points to.
|
||||||
We'll see more examples of DSTs in the rest of the course.
|
We'll see more examples of DSTs in the rest of the course.
|
||||||
|
|
||||||
|
@ -59,14 +59,14 @@ A type is `Sized` if its size is known at compile time. In other words, it's not
|
||||||
|
|
||||||
### Marker traits
|
### Marker traits
|
||||||
|
|
||||||
`Sized` is your first example of a **marker trait**.
|
`Sized` is your first example of a **marker trait**.\
|
||||||
A marker trait is a trait that doesn't require any methods to be implemented. It doesn't define any behavior.
|
A marker trait is a trait that doesn't require any methods to be implemented. It doesn't define any behavior.
|
||||||
It only serves to **mark** a type as having certain properties.
|
It only serves to **mark** a type as having certain properties.
|
||||||
The mark is then leveraged by the compiler to enable certain behaviors or optimizations.
|
The mark is then leveraged by the compiler to enable certain behaviors or optimizations.
|
||||||
|
|
||||||
### Auto traits
|
### Auto traits
|
||||||
|
|
||||||
In particular, `Sized` is also an **auto trait**.
|
In particular, `Sized` is also an **auto trait**.\
|
||||||
You don't need to implement it explicitly; the compiler implements it automatically for you
|
You don't need to implement it explicitly; the compiler implements it automatically for you
|
||||||
based on the type's definition.
|
based on the type's definition.
|
||||||
|
|
||||||
|
@ -74,7 +74,7 @@ based on the type's definition.
|
||||||
|
|
||||||
All the types we've seen so far are `Sized`: `u32`, `String`, `bool`, etc.
|
All the types we've seen so far are `Sized`: `u32`, `String`, `bool`, etc.
|
||||||
|
|
||||||
`str`, as we just saw, is not `Sized`.
|
`str`, as we just saw, is not `Sized`.\
|
||||||
`&str` is `Sized` though! We know its size at compile time: two `usize`s, one for the pointer
|
`&str` is `Sized` though! We know its size at compile time: two `usize`s, one for the pointer
|
||||||
and one for the length.
|
and one for the length.
|
||||||
|
|
||||||
|
|
|
@ -20,7 +20,7 @@ impl Ticket {
|
||||||
}
|
}
|
||||||
```
|
```
|
||||||
|
|
||||||
We've also seen that string literals (such as `"A title"`) are of type `&str`.
|
We've also seen that string literals (such as `"A title"`) are of type `&str`.\
|
||||||
We have a type mismatch here: a `String` is expected, but we have a `&str`.
|
We have a type mismatch here: a `String` is expected, but we have a `&str`.
|
||||||
No magical coercion will come to save us this time; we need **to perform a conversion**.
|
No magical coercion will come to save us this time; we need **to perform a conversion**.
|
||||||
|
|
||||||
|
@ -99,18 +99,18 @@ you can't use them with other traits.
|
||||||
## `&str` to `String`
|
## `&str` to `String`
|
||||||
|
|
||||||
In [`std`'s documentation](https://doc.rust-lang.org/std/convert/trait.From.html#implementors)
|
In [`std`'s documentation](https://doc.rust-lang.org/std/convert/trait.From.html#implementors)
|
||||||
you can see which `std` types implement the `From` trait.
|
you can see which `std` types implement the `From` trait.\
|
||||||
You'll find that `String` implements `From<&str> for String`. Thus, we can write:
|
You'll find that `String` implements `From<&str> for String`. Thus, we can write:
|
||||||
|
|
||||||
```rust
|
```rust
|
||||||
let title = String::from("A title");
|
let title = String::from("A title");
|
||||||
```
|
```
|
||||||
|
|
||||||
We've been primarily using `.into()`, though.
|
We've been primarily using `.into()`, though.\
|
||||||
If you check out the [implementors of `Into`](https://doc.rust-lang.org/std/convert/trait.Into.html#implementors)
|
If you check out the [implementors of `Into`](https://doc.rust-lang.org/std/convert/trait.Into.html#implementors)
|
||||||
you won't find `Into<&str> for String`. What's going on?
|
you won't find `Into<&str> for String`. What's going on?
|
||||||
|
|
||||||
`From` and `Into` are **dual traits**.
|
`From` and `Into` are **dual traits**.\
|
||||||
In particular, `Into` is implemented for any type that implements `From` using a **blanket implementation**:
|
In particular, `Into` is implemented for any type that implements `From` using a **blanket implementation**:
|
||||||
|
|
||||||
```rust
|
```rust
|
||||||
|
@ -129,7 +129,7 @@ we can write `let title = "A title".into();`.
|
||||||
|
|
||||||
## `.into()`
|
## `.into()`
|
||||||
|
|
||||||
Every time you see `.into()`, you're witnessing a conversion between types.
|
Every time you see `.into()`, you're witnessing a conversion between types.\
|
||||||
What's the target type, though?
|
What's the target type, though?
|
||||||
|
|
||||||
In most cases, the target type is either:
|
In most cases, the target type is either:
|
||||||
|
|
|
@ -14,8 +14,8 @@ pub trait Deref {
|
||||||
}
|
}
|
||||||
```
|
```
|
||||||
|
|
||||||
They both feature type parameters.
|
They both feature type parameters.\
|
||||||
In the case of `From`, it's a generic parameter, `T`.
|
In the case of `From`, it's a generic parameter, `T`.\
|
||||||
In the case of `Deref`, it's an associated type, `Target`.
|
In the case of `Deref`, it's an associated type, `Target`.
|
||||||
|
|
||||||
What's the difference? Why use one over the other?
|
What's the difference? Why use one over the other?
|
||||||
|
@ -27,7 +27,7 @@ only deref to `str`.
|
||||||
It's about avoiding ambiguity: if you could implement `Deref` multiple times for a type,
|
It's about avoiding ambiguity: if you could implement `Deref` multiple times for a type,
|
||||||
which `Target` type should the compiler choose when you call a `&self` method?
|
which `Target` type should the compiler choose when you call a `&self` method?
|
||||||
|
|
||||||
That's why `Deref` uses an associated type, `Target`.
|
That's why `Deref` uses an associated type, `Target`.\
|
||||||
An associated type is uniquely determined **by the trait implementation**.
|
An associated type is uniquely determined **by the trait implementation**.
|
||||||
Since you can't implement `Deref` more than once, you'll only be able to specify one `Target` for a given type
|
Since you can't implement `Deref` more than once, you'll only be able to specify one `Target` for a given type
|
||||||
and there won't be any ambiguity.
|
and there won't be any ambiguity.
|
||||||
|
@ -51,7 +51,7 @@ impl From<u16> for WrappingU32 {
|
||||||
}
|
}
|
||||||
```
|
```
|
||||||
|
|
||||||
This works because `From<u16>` and `From<u32>` are considered **different traits**.
|
This works because `From<u16>` and `From<u32>` are considered **different traits**.\
|
||||||
There is no ambiguity: the compiler can determine which implementation to use based on type of the value being converted.
|
There is no ambiguity: the compiler can determine which implementation to use based on type of the value being converted.
|
||||||
|
|
||||||
## Case study: `Add`
|
## Case study: `Add`
|
||||||
|
@ -73,7 +73,7 @@ It uses both mechanisms:
|
||||||
|
|
||||||
### `RHS`
|
### `RHS`
|
||||||
|
|
||||||
`RHS` is a generic parameter to allow for different types to be added together.
|
`RHS` is a generic parameter to allow for different types to be added together.\
|
||||||
For example, you'll find these two implementations in the standard library:
|
For example, you'll find these two implementations in the standard library:
|
||||||
|
|
||||||
```rust
|
```rust
|
||||||
|
@ -125,7 +125,7 @@ impl Add<&u32> for &u32 {
|
||||||
}
|
}
|
||||||
```
|
```
|
||||||
|
|
||||||
The type they're implementing the trait for is `&u32`, but the result of the addition is `u32`.
|
The type they're implementing the trait for is `&u32`, but the result of the addition is `u32`.\
|
||||||
It would be impossible[^flexible] to provide this implementation if `add` had to return `Self`, i.e. `&u32` in this case.
|
It would be impossible[^flexible] to provide this implementation if `add` had to return `Self`, i.e. `&u32` in this case.
|
||||||
`Output` lets `std` decouple the implementor from the return type, thus supporting this case.
|
`Output` lets `std` decouple the implementor from the return type, thus supporting this case.
|
||||||
|
|
||||||
|
@ -148,4 +148,3 @@ To recap:
|
||||||
[^flexible]: Flexibility is rarely free: the trait definition is more complex due to `Output`, and implementors have to reason about
|
[^flexible]: Flexibility is rarely free: the trait definition is more complex due to `Output`, and implementors have to reason about
|
||||||
what they want to return. The trade-off is only justified if that flexibility is actually needed. Keep that in mind
|
what they want to return. The trade-off is only justified if that flexibility is actually needed. Keep that in mind
|
||||||
when designing your own traits.
|
when designing your own traits.
|
||||||
|
|
||||||
|
|
|
@ -1,12 +1,12 @@
|
||||||
# Copying values, pt. 1
|
# Copying values, pt. 1
|
||||||
|
|
||||||
In the previous chapter we introduced ownership and borrowing.
|
In the previous chapter we introduced ownership and borrowing.\
|
||||||
We stated, in particular, that:
|
We stated, in particular, that:
|
||||||
|
|
||||||
- Every value in Rust has a single owner at any given time.
|
- Every value in Rust has a single owner at any given time.
|
||||||
- When a function takes ownership of a value ("it consumes it"), the caller can't use that value anymore.
|
- When a function takes ownership of a value ("it consumes it"), the caller can't use that value anymore.
|
||||||
|
|
||||||
These restrictions can be somewhat limiting.
|
These restrictions can be somewhat limiting.\
|
||||||
Sometimes we might have to call a function that takes ownership of a value, but we still need to use
|
Sometimes we might have to call a function that takes ownership of a value, but we still need to use
|
||||||
that value afterward.
|
that value afterward.
|
||||||
|
|
||||||
|
@ -50,7 +50,7 @@ fn example() {
|
||||||
```
|
```
|
||||||
|
|
||||||
Instead of giving ownership of `s` to `consumer`, we create a new `String` (by cloning `s`) and give
|
Instead of giving ownership of `s` to `consumer`, we create a new `String` (by cloning `s`) and give
|
||||||
that to `consumer` instead.
|
that to `consumer` instead.\
|
||||||
`s` remains valid and usable after the call to `consumer`.
|
`s` remains valid and usable after the call to `consumer`.
|
||||||
|
|
||||||
## In memory
|
## In memory
|
||||||
|
@ -92,7 +92,7 @@ If you're coming from a language like Java, you can think of `clone` as a way to
|
||||||
|
|
||||||
## Implementing `Clone`
|
## Implementing `Clone`
|
||||||
|
|
||||||
To make a type `Clone`-able, we have to implement the `Clone` trait for it.
|
To make a type `Clone`-able, we have to implement the `Clone` trait for it.\
|
||||||
You almost always implement `Clone` by deriving it:
|
You almost always implement `Clone` by deriving it:
|
||||||
|
|
||||||
```rust
|
```rust
|
||||||
|
@ -103,7 +103,7 @@ struct MyType {
|
||||||
```
|
```
|
||||||
|
|
||||||
The compiler implements `Clone` for `MyType` as you would expect: it clones each field of `MyType` individually and
|
The compiler implements `Clone` for `MyType` as you would expect: it clones each field of `MyType` individually and
|
||||||
then constructs a new `MyType` instance using the cloned fields.
|
then constructs a new `MyType` instance using the cloned fields.\
|
||||||
Remember that you can use `cargo expand` (or your IDE) to explore the code generated by `derive` macros.
|
Remember that you can use `cargo expand` (or your IDE) to explore the code generated by `derive` macros.
|
||||||
|
|
||||||
## References
|
## References
|
||||||
|
|
|
@ -26,14 +26,14 @@ pub trait Copy: Clone { }
|
||||||
It is a marker trait, just like `Sized`.
|
It is a marker trait, just like `Sized`.
|
||||||
|
|
||||||
If a type implements `Copy`, there's no need to call `.clone()` to create a new instance of the type:
|
If a type implements `Copy`, there's no need to call `.clone()` to create a new instance of the type:
|
||||||
Rust does it **implicitly** for you.
|
Rust does it **implicitly** for you.\
|
||||||
`u32` is an example of a type that implements `Copy`, which is why the example above compiles without errors:
|
`u32` is an example of a type that implements `Copy`, which is why the example above compiles without errors:
|
||||||
when `consumer(s)` is called, Rust creates a new `u32` instance by performing a **bitwise copy** of `s`,
|
when `consumer(s)` is called, Rust creates a new `u32` instance by performing a **bitwise copy** of `s`,
|
||||||
and then passes that new instance to `consumer`. It all happens behind the scenes, without you having to do anything.
|
and then passes that new instance to `consumer`. It all happens behind the scenes, without you having to do anything.
|
||||||
|
|
||||||
## What can be `Copy`?
|
## What can be `Copy`?
|
||||||
|
|
||||||
`Copy` is not equivalent to "automatic cloning", although it implies it.
|
`Copy` is not equivalent to "automatic cloning", although it implies it.\
|
||||||
Types must meet a few requirements in order to be allowed to implement `Copy`.
|
Types must meet a few requirements in order to be allowed to implement `Copy`.
|
||||||
|
|
||||||
First of all, it must implement `Clone`, since `Copy` is a subtrait of `Clone`.
|
First of all, it must implement `Clone`, since `Copy` is a subtrait of `Clone`.
|
||||||
|
@ -52,10 +52,10 @@ that performs the bitwise copy.
|
||||||
|
|
||||||
### Case study 1: `String`
|
### Case study 1: `String`
|
||||||
|
|
||||||
`String` is a type that doesn't implement `Copy`.
|
`String` is a type that doesn't implement `Copy`.\
|
||||||
Why? Because it manages an additional resource: the heap-allocated memory buffer that stores the string's data.
|
Why? Because it manages an additional resource: the heap-allocated memory buffer that stores the string's data.
|
||||||
|
|
||||||
Let's imagine that Rust allowed `String` to implement `Copy`.
|
Let's imagine that Rust allowed `String` to implement `Copy`.\
|
||||||
Then, when a new `String` instance is created by performing a bitwise copy of the original instance, both the original
|
Then, when a new `String` instance is created by performing a bitwise copy of the original instance, both the original
|
||||||
and the new instance would point to the same memory buffer:
|
and the new instance would point to the same memory buffer:
|
||||||
|
|
||||||
|
@ -84,7 +84,7 @@ violating Rust's borrowing rules.
|
||||||
|
|
||||||
### Case study 2: `u32`
|
### Case study 2: `u32`
|
||||||
|
|
||||||
`u32` implements `Copy`. All integer types do, in fact.
|
`u32` implements `Copy`. All integer types do, in fact.\
|
||||||
An integer is "just" the bytes that represent the number in memory. There's nothing more!
|
An integer is "just" the bytes that represent the number in memory. There's nothing more!
|
||||||
If you copy those bytes, you get another perfectly valid integer instance.
|
If you copy those bytes, you get another perfectly valid integer instance.
|
||||||
Nothing bad can happen, so Rust allows it.
|
Nothing bad can happen, so Rust allows it.
|
||||||
|
@ -92,7 +92,7 @@ Nothing bad can happen, so Rust allows it.
|
||||||
### Case study 3: `&mut u32`
|
### Case study 3: `&mut u32`
|
||||||
|
|
||||||
When we introduced ownership and mutable borrows, we stated one rule quite clearly: there
|
When we introduced ownership and mutable borrows, we stated one rule quite clearly: there
|
||||||
can only ever be *one* mutable borrow of a value at any given time.
|
can only ever be _one_ mutable borrow of a value at any given time.\
|
||||||
That's why `&mut u32` doesn't implement `Copy`, even though `u32` does.
|
That's why `&mut u32` doesn't implement `Copy`, even though `u32` does.
|
||||||
|
|
||||||
If `&mut u32` implemented `Copy`, you could create multiple mutable references to
|
If `&mut u32` implemented `Copy`, you could create multiple mutable references to
|
||||||
|
|
|
@ -15,7 +15,7 @@ pub trait Drop {
|
||||||
```
|
```
|
||||||
|
|
||||||
The `Drop` trait is a mechanism for you to define _additional_ cleanup logic for your types,
|
The `Drop` trait is a mechanism for you to define _additional_ cleanup logic for your types,
|
||||||
beyond what the compiler does for you automatically.
|
beyond what the compiler does for you automatically.\
|
||||||
Whatever you put in the `drop` method will be executed when the value goes out of scope.
|
Whatever you put in the `drop` method will be executed when the value goes out of scope.
|
||||||
|
|
||||||
## `Drop` and `Copy`
|
## `Drop` and `Copy`
|
||||||
|
@ -24,7 +24,7 @@ When talking about the `Copy` trait, we said that a type can't implement `Copy`
|
||||||
manages additional resources beyond the `std::mem::size_of` bytes that it occupies in memory.
|
manages additional resources beyond the `std::mem::size_of` bytes that it occupies in memory.
|
||||||
|
|
||||||
You might wonder: how does the compiler know if a type manages additional resources?
|
You might wonder: how does the compiler know if a type manages additional resources?
|
||||||
That's right: `Drop` trait implementations!
|
That's right: `Drop` trait implementations!\
|
||||||
If your type has an explicit `Drop` implementation, the compiler will assume
|
If your type has an explicit `Drop` implementation, the compiler will assume
|
||||||
that your type has additional resources attached to it and won't allow you to implement `Copy`.
|
that your type has additional resources attached to it and won't allow you to implement `Copy`.
|
||||||
|
|
||||||
|
|
|
@ -6,7 +6,7 @@ so often when writing Rust code that they'll soon become second nature.
|
||||||
|
|
||||||
## Closing thoughts
|
## Closing thoughts
|
||||||
|
|
||||||
Traits are powerful, but don't overuse them.
|
Traits are powerful, but don't overuse them.\
|
||||||
A few guidelines to keep in mind:
|
A few guidelines to keep in mind:
|
||||||
|
|
||||||
- Don't make a function generic if it is always invoked with a single type. It introduces indirection in your
|
- Don't make a function generic if it is always invoked with a single type. It introduces indirection in your
|
||||||
|
|
|
@ -1,7 +1,7 @@
|
||||||
# Enumerations
|
# Enumerations
|
||||||
|
|
||||||
Based on the validation logic you wrote [in a previous chapter](../03_ticket_v1/02_validation.md),
|
Based on the validation logic you wrote [in a previous chapter](../03_ticket_v1/02_validation.md),
|
||||||
there are only a few valid statuses for a ticket: `To-Do`, `InProgress` and `Done`.
|
there are only a few valid statuses for a ticket: `To-Do`, `InProgress` and `Done`.\
|
||||||
This is not obvious if we look at the `status` field in the `Ticket` struct or at the type of the `status`
|
This is not obvious if we look at the `status` field in the `Ticket` struct or at the type of the `status`
|
||||||
parameter in the `new` method:
|
parameter in the `new` method:
|
||||||
|
|
||||||
|
@ -29,7 +29,7 @@ We can do better than that with **enumerations**.
|
||||||
|
|
||||||
## `enum`
|
## `enum`
|
||||||
|
|
||||||
An enumeration is a type that can have a fixed set of values, called **variants**.
|
An enumeration is a type that can have a fixed set of values, called **variants**.\
|
||||||
In Rust, you define an enumeration using the `enum` keyword:
|
In Rust, you define an enumeration using the `enum` keyword:
|
||||||
|
|
||||||
```rust
|
```rust
|
||||||
|
|
|
@ -1,6 +1,6 @@
|
||||||
# `match`
|
# `match`
|
||||||
|
|
||||||
You may be wondering—what can you actually **do** with an enum?
|
You may be wondering—what can you actually **do** with an enum?\
|
||||||
The most common operation is to **match** on it.
|
The most common operation is to **match** on it.
|
||||||
|
|
||||||
```rust
|
```rust
|
||||||
|
@ -22,13 +22,13 @@ impl Status {
|
||||||
}
|
}
|
||||||
```
|
```
|
||||||
|
|
||||||
A `match` statement that lets you compare a Rust value against a series of **patterns**.
|
A `match` statement that lets you compare a Rust value against a series of **patterns**.\
|
||||||
You can think of it as a type-level `if`. If `status` is a `Done` variant, execute the first block;
|
You can think of it as a type-level `if`. If `status` is a `Done` variant, execute the first block;
|
||||||
if it's a `InProgress` or `ToDo` variant, execute the second block.
|
if it's a `InProgress` or `ToDo` variant, execute the second block.
|
||||||
|
|
||||||
## Exhaustiveness
|
## Exhaustiveness
|
||||||
|
|
||||||
There's one key detail here: `match` is **exhaustive**. You must handle all enum variants.
|
There's one key detail here: `match` is **exhaustive**. You must handle all enum variants.\
|
||||||
If you forget to handle a variant, Rust will stop you **at compile-time** with an error.
|
If you forget to handle a variant, Rust will stop you **at compile-time** with an error.
|
||||||
|
|
||||||
E.g. if we forget to handle the `ToDo` variant:
|
E.g. if we forget to handle the `ToDo` variant:
|
||||||
|
@ -50,7 +50,7 @@ error[E0004]: non-exhaustive patterns: `ToDo` not covered
|
||||||
| ^^^^^^^^^^^^ pattern `ToDo` not covered
|
| ^^^^^^^^^^^^ pattern `ToDo` not covered
|
||||||
```
|
```
|
||||||
|
|
||||||
This is a big deal!
|
This is a big deal!\
|
||||||
Codebases evolve over time—you might add a new status down the line, e.g. `Blocked`. The Rust compiler
|
Codebases evolve over time—you might add a new status down the line, e.g. `Blocked`. The Rust compiler
|
||||||
will emit an error for every single `match` statement that's missing logic for the new variant.
|
will emit an error for every single `match` statement that's missing logic for the new variant.
|
||||||
That's why Rust developers often sing the praises of "compiler-driven refactoring"—the compiler tells you
|
That's why Rust developers often sing the praises of "compiler-driven refactoring"—the compiler tells you
|
||||||
|
|
|
@ -8,7 +8,7 @@ enum Status {
|
||||||
}
|
}
|
||||||
```
|
```
|
||||||
|
|
||||||
Our `Status` enum is what's usually called a **C-style enum**.
|
Our `Status` enum is what's usually called a **C-style enum**.\
|
||||||
Each variant is a simple label, a bit like a named constant. You can find this kind of enum in many programming
|
Each variant is a simple label, a bit like a named constant. You can find this kind of enum in many programming
|
||||||
languages, like C, C++, Java, C#, Python, etc.
|
languages, like C, C++, Java, C#, Python, etc.
|
||||||
|
|
||||||
|
@ -16,7 +16,7 @@ Rust enums can go further though. We can **attach data to each variant**.
|
||||||
|
|
||||||
## Variants
|
## Variants
|
||||||
|
|
||||||
Let's say that we want to store the name of the person who's currently working on a ticket.
|
Let's say that we want to store the name of the person who's currently working on a ticket.\
|
||||||
We would only have this information if the ticket is in progress. It wouldn't be there for a to-do ticket or
|
We would only have this information if the ticket is in progress. It wouldn't be there for a to-do ticket or
|
||||||
a done ticket.
|
a done ticket.
|
||||||
We can model this by attaching a `String` field to the `InProgress` variant:
|
We can model this by attaching a `String` field to the `InProgress` variant:
|
||||||
|
@ -31,7 +31,7 @@ enum Status {
|
||||||
}
|
}
|
||||||
```
|
```
|
||||||
|
|
||||||
`InProgress` is now a **struct-like variant**.
|
`InProgress` is now a **struct-like variant**.\
|
||||||
The syntax mirrors, in fact, the one we used to define a struct—it's just "inlined" inside the enum, as a variant.
|
The syntax mirrors, in fact, the one we used to define a struct—it's just "inlined" inside the enum, as a variant.
|
||||||
|
|
||||||
## Accessing variant data
|
## Accessing variant data
|
||||||
|
@ -55,7 +55,7 @@ error[E0609]: no field `assigned_to` on type `Status`
|
||||||
| ^^^^^^^^^^^ unknown field
|
| ^^^^^^^^^^^ unknown field
|
||||||
```
|
```
|
||||||
|
|
||||||
`assigned_to` is **variant-specific**, it's not available on all `Status` instances.
|
`assigned_to` is **variant-specific**, it's not available on all `Status` instances.\
|
||||||
To access `assigned_to`, we need to use **pattern matching**:
|
To access `assigned_to`, we need to use **pattern matching**:
|
||||||
|
|
||||||
```rust
|
```rust
|
||||||
|
@ -71,9 +71,9 @@ match status {
|
||||||
|
|
||||||
## Bindings
|
## Bindings
|
||||||
|
|
||||||
In the match pattern `Status::InProgress { assigned_to }`, `assigned_to` is a **binding**.
|
In the match pattern `Status::InProgress { assigned_to }`, `assigned_to` is a **binding**.\
|
||||||
We're **destructuring** the `Status::InProgress` variant and binding the `assigned_to` field to
|
We're **destructuring** the `Status::InProgress` variant and binding the `assigned_to` field to
|
||||||
a new variable, also named `assigned_to`.
|
a new variable, also named `assigned_to`.\
|
||||||
If we wanted, we could bind the field to a different variable name:
|
If we wanted, we could bind the field to a different variable name:
|
||||||
|
|
||||||
```rust
|
```rust
|
||||||
|
|
|
@ -61,7 +61,7 @@ as the code that precedes it.
|
||||||
|
|
||||||
## Style
|
## Style
|
||||||
|
|
||||||
Both `if let` and `let/else` are idiomatic Rust constructs.
|
Both `if let` and `let/else` are idiomatic Rust constructs.\
|
||||||
Use them as you see fit to improve the readability of your code,
|
Use them as you see fit to improve the readability of your code,
|
||||||
but don't overdo it: `match` is always there when you need it.
|
but don't overdo it: `match` is always there when you need it.
|
||||||
|
|
||||||
|
|
|
@ -1,11 +1,11 @@
|
||||||
# Nullability
|
# Nullability
|
||||||
|
|
||||||
Our implementation of the `assigned` method is fairly blunt: panicking for to-do and done tickets is far from ideal.
|
Our implementation of the `assigned` method is fairly blunt: panicking for to-do and done tickets is far from ideal.\
|
||||||
We can do better using **Rust's `Option` type**.
|
We can do better using **Rust's `Option` type**.
|
||||||
|
|
||||||
## `Option`
|
## `Option`
|
||||||
|
|
||||||
`Option` is a Rust type that represents **nullable values**.
|
`Option` is a Rust type that represents **nullable values**.\
|
||||||
It is an enum, defined in Rust's standard library:
|
It is an enum, defined in Rust's standard library:
|
||||||
|
|
||||||
```rust
|
```rust
|
||||||
|
@ -15,9 +15,9 @@ enum Option<T> {
|
||||||
}
|
}
|
||||||
```
|
```
|
||||||
|
|
||||||
`Option` encodes the idea that a value might be present (`Some(T)`) or absent (`None`).
|
`Option` encodes the idea that a value might be present (`Some(T)`) or absent (`None`).\
|
||||||
It also forces you to **explicitly handle both cases**. You'll get a compiler error if you are working with
|
It also forces you to **explicitly handle both cases**. You'll get a compiler error if you are working with
|
||||||
a nullable value and you forget to handle the `None` case.
|
a nullable value and you forget to handle the `None` case.\
|
||||||
This is a significant improvement over "implicit" nullability in other languages, where you can forget to check
|
This is a significant improvement over "implicit" nullability in other languages, where you can forget to check
|
||||||
for `null` and thus trigger a runtime error.
|
for `null` and thus trigger a runtime error.
|
||||||
|
|
||||||
|
@ -27,7 +27,7 @@ for `null` and thus trigger a runtime error.
|
||||||
|
|
||||||
### Tuple-like variants
|
### Tuple-like variants
|
||||||
|
|
||||||
`Option` has two variants: `Some(T)` and `None`.
|
`Option` has two variants: `Some(T)` and `None`.\
|
||||||
`Some` is a **tuple-like variant**: it's a variant that holds **unnamed fields**.
|
`Some` is a **tuple-like variant**: it's a variant that holds **unnamed fields**.
|
||||||
|
|
||||||
Tuple-like variants are often used when there is a single field to store, especially when we're looking at a
|
Tuple-like variants are often used when there is a single field to store, especially when we're looking at a
|
||||||
|
@ -51,7 +51,7 @@ let y = point.1;
|
||||||
|
|
||||||
### Tuples
|
### Tuples
|
||||||
|
|
||||||
It's weird say that something is tuple-like when we haven't seen tuples yet!
|
It's weird say that something is tuple-like when we haven't seen tuples yet!\
|
||||||
Tuples are another example of a primitive Rust type.
|
Tuples are another example of a primitive Rust type.
|
||||||
They group together a fixed number of values with (potentially different) types:
|
They group together a fixed number of values with (potentially different) types:
|
||||||
|
|
||||||
|
|
|
@ -52,13 +52,13 @@ Both `Ok` and `Err` are generic, allowing you to specify your own types for the
|
||||||
|
|
||||||
## No exceptions
|
## No exceptions
|
||||||
|
|
||||||
Recoverable errors in Rust are **represented as values**.
|
Recoverable errors in Rust are **represented as values**.\
|
||||||
They're just an instance of a type, being passed around and manipulated like any other value.
|
They're just an instance of a type, being passed around and manipulated like any other value.
|
||||||
This is a significant difference from other languages, such as Python or C#, where **exceptions** are used to signal errors.
|
This is a significant difference from other languages, such as Python or C#, where **exceptions** are used to signal errors.
|
||||||
|
|
||||||
Exceptions create a separate control flow path that can be hard to reason about.
|
Exceptions create a separate control flow path that can be hard to reason about.\
|
||||||
You don't know, just by looking at a function's signature, if it can throw an exception or not.
|
You don't know, just by looking at a function's signature, if it can throw an exception or not.
|
||||||
You don't know, just by looking at a function's signature, **which** exception types it can throw.
|
You don't know, just by looking at a function's signature, **which** exception types it can throw.\
|
||||||
You must either read the function's documentation or look at its implementation to find out.
|
You must either read the function's documentation or look at its implementation to find out.
|
||||||
|
|
||||||
Exception handling logic has very poor locality: the code that throws the exception is far removed from the code
|
Exception handling logic has very poor locality: the code that throws the exception is far removed from the code
|
||||||
|
@ -66,7 +66,7 @@ that catches it, and there's no direct link between the two.
|
||||||
|
|
||||||
## Fallibility is encoded in the type system
|
## Fallibility is encoded in the type system
|
||||||
|
|
||||||
Rust, with `Result`, forces you to **encode fallibility in the function's signature**.
|
Rust, with `Result`, forces you to **encode fallibility in the function's signature**.\
|
||||||
If a function can fail (and you want the caller to have a shot at handling the error), it must return a `Result`.
|
If a function can fail (and you want the caller to have a shot at handling the error), it must return a `Result`.
|
||||||
|
|
||||||
```rust
|
```rust
|
||||||
|
|
|
@ -1,11 +1,11 @@
|
||||||
# Unwrapping
|
# Unwrapping
|
||||||
|
|
||||||
`Ticket::new` now returns a `Result` instead of panicking on invalid inputs.
|
`Ticket::new` now returns a `Result` instead of panicking on invalid inputs.\
|
||||||
What does this mean for the caller?
|
What does this mean for the caller?
|
||||||
|
|
||||||
## Failures can't be (implicitly) ignored
|
## Failures can't be (implicitly) ignored
|
||||||
|
|
||||||
Unlike exceptions, Rust's `Result` forces you to **handle errors at the call site**.
|
Unlike exceptions, Rust's `Result` forces you to **handle errors at the call site**.\
|
||||||
If you call a function that returns a `Result`, Rust won't allow you to implicitly ignore the error case.
|
If you call a function that returns a `Result`, Rust won't allow you to implicitly ignore the error case.
|
||||||
|
|
||||||
```rust
|
```rust
|
||||||
|
|
|
@ -1,6 +1,6 @@
|
||||||
# Error enums
|
# Error enums
|
||||||
|
|
||||||
Your solution to the previous exercise may have felt awkward: matching on strings is not ideal!
|
Your solution to the previous exercise may have felt awkward: matching on strings is not ideal!\
|
||||||
A colleague might rework the error messages returned by `Ticket::new` (e.g. to improve readability) and,
|
A colleague might rework the error messages returned by `Ticket::new` (e.g. to improve readability) and,
|
||||||
all of a sudden, your calling code would break.
|
all of a sudden, your calling code would break.
|
||||||
|
|
||||||
|
@ -22,7 +22,7 @@ enum U32ParseError {
|
||||||
```
|
```
|
||||||
|
|
||||||
Using an error enum, you're encoding the different error cases in the type system—they become part of the
|
Using an error enum, you're encoding the different error cases in the type system—they become part of the
|
||||||
signature of the fallible function.
|
signature of the fallible function.\
|
||||||
This simplifies error handling for the caller, as they can use a `match` expression to react to the different
|
This simplifies error handling for the caller, as they can use a `match` expression to react to the different
|
||||||
error cases:
|
error cases:
|
||||||
|
|
||||||
|
|
|
@ -3,7 +3,7 @@
|
||||||
## Error reporting
|
## Error reporting
|
||||||
|
|
||||||
In the previous exercise you had to destructure the `InvalidTitle` variant to extract the error message and
|
In the previous exercise you had to destructure the `InvalidTitle` variant to extract the error message and
|
||||||
pass it to the `panic!` macro.
|
pass it to the `panic!` macro.\
|
||||||
This is a (rudimentary) example of **error reporting**: transforming an error type into a representation that can be
|
This is a (rudimentary) example of **error reporting**: transforming an error type into a representation that can be
|
||||||
shown to a user, a service operator, or a developer.
|
shown to a user, a service operator, or a developer.
|
||||||
|
|
||||||
|
@ -46,8 +46,8 @@ pub trait Display {
|
||||||
}
|
}
|
||||||
```
|
```
|
||||||
|
|
||||||
The difference is in their *purpose*: `Display` returns a representation that's meant for "end-users",
|
The difference is in their _purpose_: `Display` returns a representation that's meant for "end-users",
|
||||||
while `Debug` provides a low-level representation that's more suitable to developers and service operators.
|
while `Debug` provides a low-level representation that's more suitable to developers and service operators.\
|
||||||
That's why `Debug` can be automatically implemented using the `#[derive(Debug)]` attribute, while `Display`
|
That's why `Debug` can be automatically implemented using the `#[derive(Debug)]` attribute, while `Display`
|
||||||
**requires** a manual implementation.
|
**requires** a manual implementation.
|
||||||
|
|
||||||
|
|
|
@ -1,10 +1,10 @@
|
||||||
# Libraries and binaries
|
# Libraries and binaries
|
||||||
|
|
||||||
It took a bit of code to implement the `Error` trait for `TicketNewError`, didn't it?
|
It took a bit of code to implement the `Error` trait for `TicketNewError`, didn't it?\
|
||||||
A manual `Display` implementation, plus an `Error` impl block.
|
A manual `Display` implementation, plus an `Error` impl block.
|
||||||
|
|
||||||
We can remove some of the boilerplate by using [`thiserror`](https://docs.rs/thiserror/latest/thiserror/),
|
We can remove some of the boilerplate by using [`thiserror`](https://docs.rs/thiserror/latest/thiserror/),
|
||||||
a Rust crate that provides a **procedural macro** to simplify the creation of custom error types.
|
a Rust crate that provides a **procedural macro** to simplify the creation of custom error types.\
|
||||||
But we're getting ahead of ourselves: `thiserror` is a third-party crate, it'd be our first dependency!
|
But we're getting ahead of ourselves: `thiserror` is a third-party crate, it'd be our first dependency!
|
||||||
|
|
||||||
Let's take a step back to talk about Rust's packaging system before we dive into dependencies.
|
Let's take a step back to talk about Rust's packaging system before we dive into dependencies.
|
||||||
|
@ -18,18 +18,18 @@ Go check the `Cargo.toml` file in the directory of this section's exercise!
|
||||||
|
|
||||||
## What is a crate?
|
## What is a crate?
|
||||||
|
|
||||||
Inside a package, you can have one or more **crates**, also known as **targets**.
|
Inside a package, you can have one or more **crates**, also known as **targets**.\
|
||||||
The two most common crate types are **binary crates** and **library crates**.
|
The two most common crate types are **binary crates** and **library crates**.
|
||||||
|
|
||||||
### Binaries
|
### Binaries
|
||||||
|
|
||||||
A binary is a program that can be compiled to an **executable file**.
|
A binary is a program that can be compiled to an **executable file**.\
|
||||||
It must include a function named `main`—the program's entry point. `main` is invoked when the program is executed.
|
It must include a function named `main`—the program's entry point. `main` is invoked when the program is executed.
|
||||||
|
|
||||||
### Libraries
|
### Libraries
|
||||||
|
|
||||||
Libraries, on the other hand, are not executable on their own. You can't _run_ a library,
|
Libraries, on the other hand, are not executable on their own. You can't _run_ a library,
|
||||||
but you can _import its code_ from another package that depends on it.
|
but you can _import its code_ from another package that depends on it.\
|
||||||
A library groups together code (i.e. functions, types, etc.) that can be leveraged by other packages as a **dependency**.
|
A library groups together code (i.e. functions, types, etc.) that can be leveraged by other packages as a **dependency**.
|
||||||
|
|
||||||
All the exercises you've solved so far have been structured as libraries, with a test suite attached to them.
|
All the exercises you've solved so far have been structured as libraries, with a test suite attached to them.
|
||||||
|
|
|
@ -1,6 +1,6 @@
|
||||||
# Dependencies
|
# Dependencies
|
||||||
|
|
||||||
A package can depend on other packages by listing them in the `[dependencies]` section of its `Cargo.toml` file.
|
A package can depend on other packages by listing them in the `[dependencies]` section of its `Cargo.toml` file.\
|
||||||
The most common way to specify a dependency is by providing its name and version:
|
The most common way to specify a dependency is by providing its name and version:
|
||||||
|
|
||||||
```toml
|
```toml
|
||||||
|
@ -43,7 +43,7 @@ details on where you can get dependencies from and how to specify them in your `
|
||||||
## Dev dependencies
|
## Dev dependencies
|
||||||
|
|
||||||
You can also specify dependencies that are only needed for development—i.e. they only get pulled in when you're
|
You can also specify dependencies that are only needed for development—i.e. they only get pulled in when you're
|
||||||
running `cargo test`.
|
running `cargo test`.\
|
||||||
They go in the `[dev-dependencies]` section of your `Cargo.toml` file:
|
They go in the `[dev-dependencies]` section of your `Cargo.toml` file:
|
||||||
|
|
||||||
```toml
|
```toml
|
||||||
|
|
|
@ -1,11 +1,11 @@
|
||||||
# `thiserror`
|
# `thiserror`
|
||||||
|
|
||||||
That was a bit of detour, wasn't it? But a necessary one!
|
That was a bit of detour, wasn't it? But a necessary one!\
|
||||||
Let's get back on track now: custom error types and `thiserror`.
|
Let's get back on track now: custom error types and `thiserror`.
|
||||||
|
|
||||||
## Custom error types
|
## Custom error types
|
||||||
|
|
||||||
We've seen how to implement the `Error` trait "manually" for a custom error type.
|
We've seen how to implement the `Error` trait "manually" for a custom error type.\
|
||||||
Imagine that you have to do this for most error types in your codebase. That's a lot of boilerplate, isn't it?
|
Imagine that you have to do this for most error types in your codebase. That's a lot of boilerplate, isn't it?
|
||||||
|
|
||||||
We can remove some of the boilerplate by using [`thiserror`](https://docs.rs/thiserror/latest/thiserror/),
|
We can remove some of the boilerplate by using [`thiserror`](https://docs.rs/thiserror/latest/thiserror/),
|
||||||
|
@ -23,12 +23,12 @@ enum TicketNewError {
|
||||||
|
|
||||||
## You can write your own macros
|
## You can write your own macros
|
||||||
|
|
||||||
All the `derive` macros we've seen so far were provided by the Rust standard library.
|
All the `derive` macros we've seen so far were provided by the Rust standard library.\
|
||||||
`thiserror::Error` is the first example of a **third-party** `derive` macro.
|
`thiserror::Error` is the first example of a **third-party** `derive` macro.
|
||||||
|
|
||||||
`derive` macros are a subset of **procedural macros**, a way to generate Rust code at compile time.
|
`derive` macros are a subset of **procedural macros**, a way to generate Rust code at compile time.
|
||||||
We won't get into the details of how to write a procedural macro in this course, but it's important
|
We won't get into the details of how to write a procedural macro in this course, but it's important
|
||||||
to know that you can write your own!
|
to know that you can write your own!\
|
||||||
A topic to approach in a more advanced Rust course.
|
A topic to approach in a more advanced Rust course.
|
||||||
|
|
||||||
## Custom syntax
|
## Custom syntax
|
||||||
|
|
|
@ -1,7 +1,7 @@
|
||||||
# `TryFrom` and `TryInto`
|
# `TryFrom` and `TryInto`
|
||||||
|
|
||||||
In the previous chapter we looked at the [`From` and `Into` traits](../04_traits/09_from.md),
|
In the previous chapter we looked at the [`From` and `Into` traits](../04_traits/09_from.md),
|
||||||
Rust's idiomatic interfaces for **infallible** type conversions.
|
Rust's idiomatic interfaces for **infallible** type conversions.\
|
||||||
But what if the conversion is not guaranteed to succeed?
|
But what if the conversion is not guaranteed to succeed?
|
||||||
|
|
||||||
We now know enough about errors to discuss the **fallible** counterparts of `From` and `Into`:
|
We now know enough about errors to discuss the **fallible** counterparts of `From` and `Into`:
|
||||||
|
@ -23,7 +23,7 @@ pub trait TryInto<T>: Sized {
|
||||||
}
|
}
|
||||||
```
|
```
|
||||||
|
|
||||||
The main difference between `From`/`Into` and `TryFrom`/`TryInto` is that the latter return a `Result` type.
|
The main difference between `From`/`Into` and `TryFrom`/`TryInto` is that the latter return a `Result` type.\
|
||||||
This allows the conversion to fail, returning an error instead of panicking.
|
This allows the conversion to fail, returning an error instead of panicking.
|
||||||
|
|
||||||
## `Self::Error`
|
## `Self::Error`
|
||||||
|
@ -36,7 +36,7 @@ being attempted.
|
||||||
|
|
||||||
## Duality
|
## Duality
|
||||||
|
|
||||||
Just like `From` and `Into`, `TryFrom` and `TryInto` are dual traits.
|
Just like `From` and `Into`, `TryFrom` and `TryInto` are dual traits.\
|
||||||
If you implement `TryFrom` for a type, you get `TryInto` for free.
|
If you implement `TryFrom` for a type, you get `TryInto` for free.
|
||||||
|
|
||||||
## References
|
## References
|
||||||
|
|
|
@ -11,7 +11,7 @@ pub trait Error: Debug + Display {
|
||||||
}
|
}
|
||||||
```
|
```
|
||||||
|
|
||||||
The `source` method is a way to access the **error cause**, if any.
|
The `source` method is a way to access the **error cause**, if any.\
|
||||||
Errors are often chained, meaning that one error is the cause of another: you have a high-level error (e.g.
|
Errors are often chained, meaning that one error is the cause of another: you have a high-level error (e.g.
|
||||||
cannot connect to the database) that is caused by a lower-level error (e.g. can't resolve the database hostname).
|
cannot connect to the database) that is caused by a lower-level error (e.g. can't resolve the database hostname).
|
||||||
The `source` method allows you to "walk" the full chain of errors, often used when capturing error context in logs.
|
The `source` method allows you to "walk" the full chain of errors, often used when capturing error context in logs.
|
||||||
|
@ -19,7 +19,7 @@ The `source` method allows you to "walk" the full chain of errors, often used wh
|
||||||
## Implementing `source`
|
## Implementing `source`
|
||||||
|
|
||||||
The `Error` trait provides a default implementation that always returns `None` (i.e. no underlying cause). That's why
|
The `Error` trait provides a default implementation that always returns `None` (i.e. no underlying cause). That's why
|
||||||
you didn't have to care about `source` in the previous exercises.
|
you didn't have to care about `source` in the previous exercises.\
|
||||||
You can override this default implementation to provide a cause for your error type.
|
You can override this default implementation to provide a cause for your error type.
|
||||||
|
|
||||||
```rust
|
```rust
|
||||||
|
@ -48,7 +48,7 @@ We then override the `source` method to return this source when called.
|
||||||
|
|
||||||
## `&(dyn Error + 'static)`
|
## `&(dyn Error + 'static)`
|
||||||
|
|
||||||
What's this `&(dyn Error + 'static)` type?
|
What's this `&(dyn Error + 'static)` type?\
|
||||||
Let's unpack it:
|
Let's unpack it:
|
||||||
|
|
||||||
- `dyn Error` is a **trait object**. It's a way to refer to any type that implements the `Error` trait.
|
- `dyn Error` is a **trait object**. It's a way to refer to any type that implements the `Error` trait.
|
||||||
|
@ -106,7 +106,7 @@ Don't worry too much about either of these concepts for now. We'll cover them in
|
||||||
|
|
||||||
## The `?` operator
|
## The `?` operator
|
||||||
|
|
||||||
The `?` operator is a shorthand for propagating errors.
|
The `?` operator is a shorthand for propagating errors.\
|
||||||
When used in a function that returns a `Result`, it will return early with an error if the `Result` is `Err`.
|
When used in a function that returns a `Result`, it will return early with an error if the `Result` is `Err`.
|
||||||
|
|
||||||
For example:
|
For example:
|
||||||
|
@ -145,7 +145,7 @@ fn read_file() -> Result<String, std::io::Error> {
|
||||||
}
|
}
|
||||||
```
|
```
|
||||||
|
|
||||||
You can use the `?` operator to shorten your error handling code significantly.
|
You can use the `?` operator to shorten your error handling code significantly.\
|
||||||
In particular, the `?` operator will automatically convert the error type of the fallible operation into the error type
|
In particular, the `?` operator will automatically convert the error type of the fallible operation into the error type
|
||||||
of the function, if a conversion is possible (i.e. if there is a suitable `From` implementation)
|
of the function, if a conversion is possible (i.e. if there is a suitable `From` implementation)
|
||||||
|
|
||||||
|
|
|
@ -1,11 +1,11 @@
|
||||||
# Wrapping up
|
# Wrapping up
|
||||||
|
|
||||||
When it comes to domain modelling, the devil is in the details.
|
When it comes to domain modelling, the devil is in the details.\
|
||||||
Rust offers a wide range of tools to help you represent the constraints of your domain directly in the type system,
|
Rust offers a wide range of tools to help you represent the constraints of your domain directly in the type system,
|
||||||
but it takes some practice to get it right and write code that looks idiomatic.
|
but it takes some practice to get it right and write code that looks idiomatic.
|
||||||
|
|
||||||
Let's close the chapter with one final refinement of our `Ticket` model.
|
Let's close the chapter with one final refinement of our `Ticket` model.\
|
||||||
We'll introduce a new type for each of the fields in `Ticket` to encapsulate the respective constraints.
|
We'll introduce a new type for each of the fields in `Ticket` to encapsulate the respective constraints.\
|
||||||
Every time someone accesses a `Ticket` field, they'll get back a value that's guaranteed to be valid—i.e. a
|
Every time someone accesses a `Ticket` field, they'll get back a value that's guaranteed to be valid—i.e. a
|
||||||
`TicketTitle` instead of a `String`. They won't have to worry about the title being empty elsewhere in the code:
|
`TicketTitle` instead of a `String`. They won't have to worry about the title being empty elsewhere in the code:
|
||||||
as long as they have a `TicketTitle`, they know it's valid **by construction**.
|
as long as they have a `TicketTitle`, they know it's valid **by construction**.
|
||||||
|
|
|
@ -8,7 +8,7 @@ What does Rust have to offer in this regard?
|
||||||
|
|
||||||
## Arrays
|
## Arrays
|
||||||
|
|
||||||
A first attempt could be to use an **array**.
|
A first attempt could be to use an **array**.\
|
||||||
Arrays in Rust are fixed-size collections of elements of the same type.
|
Arrays in Rust are fixed-size collections of elements of the same type.
|
||||||
|
|
||||||
Here's how you can define an array:
|
Here's how you can define an array:
|
||||||
|
@ -18,7 +18,7 @@ Here's how you can define an array:
|
||||||
let numbers: [u32; 3] = [1, 2, 3];
|
let numbers: [u32; 3] = [1, 2, 3];
|
||||||
```
|
```
|
||||||
|
|
||||||
This creates an array of 3 integers, initialized with the values `1`, `2`, and `3`.
|
This creates an array of 3 integers, initialized with the values `1`, `2`, and `3`.\
|
||||||
The type of the array is `[u32; 3]`, which reads as "an array of `u32`s with a length of 3".
|
The type of the array is `[u32; 3]`, which reads as "an array of `u32`s with a length of 3".
|
||||||
|
|
||||||
### Accessing elements
|
### Accessing elements
|
||||||
|
@ -31,7 +31,7 @@ let second = numbers[1];
|
||||||
let third = numbers[2];
|
let third = numbers[2];
|
||||||
```
|
```
|
||||||
|
|
||||||
The index must be of type `usize`.
|
The index must be of type `usize`.\
|
||||||
Arrays are **zero-indexed**, like everything in Rust. You've seen this before with string slices and field indexing in
|
Arrays are **zero-indexed**, like everything in Rust. You've seen this before with string slices and field indexing in
|
||||||
tuples/tuple-like variants.
|
tuples/tuple-like variants.
|
||||||
|
|
||||||
|
@ -45,7 +45,7 @@ let fourth = numbers[3]; // This will panic
|
||||||
```
|
```
|
||||||
|
|
||||||
This is enforced at runtime using **bounds checking**. It comes with a small performance overhead, but it's how
|
This is enforced at runtime using **bounds checking**. It comes with a small performance overhead, but it's how
|
||||||
Rust prevents buffer overflows.
|
Rust prevents buffer overflows.\
|
||||||
In some scenarios the Rust compiler can optimize away bounds checks, especially if iterators are involved—we'll speak
|
In some scenarios the Rust compiler can optimize away bounds checks, especially if iterators are involved—we'll speak
|
||||||
more about this later on.
|
more about this later on.
|
||||||
|
|
||||||
|
@ -77,5 +77,5 @@ Stack: | 1 | 2 | 3 |
|
||||||
```
|
```
|
||||||
|
|
||||||
In other words, the size of an array is `std::mem::size_of::<T>() * N`, where `T` is the type of the elements and `N` is
|
In other words, the size of an array is `std::mem::size_of::<T>() * N`, where `T` is the type of the elements and `N` is
|
||||||
the number of elements.
|
the number of elements.\
|
||||||
You can access and replace each element in `O(1)` time.
|
You can access and replace each element in `O(1)` time.
|
|
@ -22,7 +22,7 @@ This is where `Vec` comes in.
|
||||||
|
|
||||||
## `Vec`
|
## `Vec`
|
||||||
|
|
||||||
`Vec` is a growable array type, provided by the standard library.
|
`Vec` is a growable array type, provided by the standard library.\
|
||||||
You can create an empty array using the `Vec::new` function:
|
You can create an empty array using the `Vec::new` function:
|
||||||
|
|
||||||
```rust
|
```rust
|
||||||
|
@ -37,7 +37,7 @@ numbers.push(2);
|
||||||
numbers.push(3);
|
numbers.push(3);
|
||||||
```
|
```
|
||||||
|
|
||||||
New values are added to the end of the vector.
|
New values are added to the end of the vector.\
|
||||||
You can also create an initialized vector using the `vec!` macro, if you know the values at creation time:
|
You can also create an initialized vector using the `vec!` macro, if you know the values at creation time:
|
||||||
|
|
||||||
```rust
|
```rust
|
||||||
|
@ -55,7 +55,7 @@ let second = numbers[1];
|
||||||
let third = numbers[2];
|
let third = numbers[2];
|
||||||
```
|
```
|
||||||
|
|
||||||
The index must be of type `usize`.
|
The index must be of type `usize`.\
|
||||||
You can also use the `get` method, which returns an `Option<&T>`:
|
You can also use the `get` method, which returns an `Option<&T>`:
|
||||||
|
|
||||||
```rust
|
```rust
|
||||||
|
@ -70,7 +70,7 @@ Access is bounds-checked, just element access with arrays. It has O(1) complexit
|
||||||
|
|
||||||
## Memory layout
|
## Memory layout
|
||||||
|
|
||||||
`Vec` is a heap-allocated data structure.
|
`Vec` is a heap-allocated data structure.\
|
||||||
When you create a `Vec`, it allocates memory on the heap to store the elements.
|
When you create a `Vec`, it allocates memory on the heap to store the elements.
|
||||||
|
|
||||||
If you run the following code:
|
If you run the following code:
|
||||||
|
@ -102,7 +102,7 @@ Heap: | 1 | 2 | ? |
|
||||||
- The **length** of the vector, i.e. how many elements are in the vector.
|
- The **length** of the vector, i.e. how many elements are in the vector.
|
||||||
- The **capacity** of the vector, i.e. the number of elements that can fit in the space reserved on the heap.
|
- The **capacity** of the vector, i.e. the number of elements that can fit in the space reserved on the heap.
|
||||||
|
|
||||||
This layout should look familiar: it's exactly the same as `String`!
|
This layout should look familiar: it's exactly the same as `String`!\
|
||||||
That's not a coincidence: `String` is defined as a vector of bytes, `Vec<u8>`, under the hood:
|
That's not a coincidence: `String` is defined as a vector of bytes, `Vec<u8>`, under the hood:
|
||||||
|
|
||||||
```rust
|
```rust
|
||||||
|
|
|
@ -11,7 +11,7 @@ numbers.push(3); // Max capacity reached
|
||||||
numbers.push(4); // What happens here?
|
numbers.push(4); // What happens here?
|
||||||
```
|
```
|
||||||
|
|
||||||
The `Vec` will **resize** itself.
|
The `Vec` will **resize** itself.\
|
||||||
It will ask the allocator for a new (larger) chunk of heap memory, copy the elements over, and deallocate the old memory.
|
It will ask the allocator for a new (larger) chunk of heap memory, copy the elements over, and deallocate the old memory.
|
||||||
|
|
||||||
This operation can be expensive, as it involves a new memory allocation and copying all existing elements.
|
This operation can be expensive, as it involves a new memory allocation and copying all existing elements.
|
||||||
|
@ -19,7 +19,7 @@ This operation can be expensive, as it involves a new memory allocation and copy
|
||||||
## `Vec::with_capacity`
|
## `Vec::with_capacity`
|
||||||
|
|
||||||
If you have a rough idea of how many elements you'll store in a `Vec`, you can use the `Vec::with_capacity`
|
If you have a rough idea of how many elements you'll store in a `Vec`, you can use the `Vec::with_capacity`
|
||||||
method to pre-allocate enough memory upfront.
|
method to pre-allocate enough memory upfront.\
|
||||||
This can avoid a new allocation when the `Vec` grows, but it may waste memory if you overestimate actual usage.
|
This can avoid a new allocation when the `Vec` grows, but it may waste memory if you overestimate actual usage.
|
||||||
|
|
||||||
Evaluate on a case-by-case basis.
|
Evaluate on a case-by-case basis.
|
||||||
|
|
|
@ -35,7 +35,7 @@ loop {
|
||||||
}
|
}
|
||||||
```
|
```
|
||||||
|
|
||||||
`loop` is another looping construct, on top of `for` and `while`.
|
`loop` is another looping construct, on top of `for` and `while`.\
|
||||||
A `loop` block will run forever, unless you explicitly `break` out of it.
|
A `loop` block will run forever, unless you explicitly `break` out of it.
|
||||||
|
|
||||||
## `Iterator` trait
|
## `Iterator` trait
|
||||||
|
@ -53,7 +53,7 @@ trait Iterator {
|
||||||
|
|
||||||
The `Item` associated type specifies the type of the values produced by the iterator.
|
The `Item` associated type specifies the type of the values produced by the iterator.
|
||||||
|
|
||||||
`next` returns the next value in the sequence.
|
`next` returns the next value in the sequence.\
|
||||||
It returns `Some(value)` if there's a value to return, and `None` when there isn't.
|
It returns `Some(value)` if there's a value to return, and `None` when there isn't.
|
||||||
|
|
||||||
Be careful: there is no guarantee that an iterator is exhausted when it returns `None`. That's only
|
Be careful: there is no guarantee that an iterator is exhausted when it returns `None`. That's only
|
||||||
|
@ -62,7 +62,7 @@ guaranteed if the iterator implements the (more restrictive)
|
||||||
|
|
||||||
## `IntoIterator` trait
|
## `IntoIterator` trait
|
||||||
|
|
||||||
Not all types implement `Iterator`, but many can be converted into a type that does.
|
Not all types implement `Iterator`, but many can be converted into a type that does.\
|
||||||
That's where the `IntoIterator` trait comes in:
|
That's where the `IntoIterator` trait comes in:
|
||||||
|
|
||||||
```rust
|
```rust
|
||||||
|
@ -73,7 +73,7 @@ trait IntoIterator {
|
||||||
}
|
}
|
||||||
```
|
```
|
||||||
|
|
||||||
The `into_iter` method consumes the original value and returns an iterator over its elements.
|
The `into_iter` method consumes the original value and returns an iterator over its elements.\
|
||||||
A type can only have one implementation of `IntoIterator`: there can be no ambiguity as to what `for` should desugar to.
|
A type can only have one implementation of `IntoIterator`: there can be no ambiguity as to what `for` should desugar to.
|
||||||
|
|
||||||
One detail: every type that implements `Iterator` automatically implements `IntoIterator` as well.
|
One detail: every type that implements `Iterator` automatically implements `IntoIterator` as well.
|
||||||
|
@ -81,7 +81,7 @@ They just return themselves from `into_iter`!
|
||||||
|
|
||||||
## Bounds checks
|
## Bounds checks
|
||||||
|
|
||||||
Iterating over iterators has a nice side effect: you can't go out of bounds, by design.
|
Iterating over iterators has a nice side effect: you can't go out of bounds, by design.\
|
||||||
This allows Rust to remove bounds checks from the generated machine code, making iteration faster.
|
This allows Rust to remove bounds checks from the generated machine code, making iteration faster.
|
||||||
|
|
||||||
In other words,
|
In other words,
|
||||||
|
|
|
@ -21,7 +21,7 @@ for n in numbers.iter() {
|
||||||
```
|
```
|
||||||
|
|
||||||
This pattern can be simplified by implementing `IntoIterator` for a **reference to the collection**.
|
This pattern can be simplified by implementing `IntoIterator` for a **reference to the collection**.
|
||||||
In our example above, that would be `&Vec<Ticket>`.
|
In our example above, that would be `&Vec<Ticket>`.\
|
||||||
The standard library does this, that's why the following code works:
|
The standard library does this, that's why the following code works:
|
||||||
|
|
||||||
```rust
|
```rust
|
||||||
|
|
|
@ -16,8 +16,8 @@ impl IntoIterator for &TicketStore {
|
||||||
}
|
}
|
||||||
```
|
```
|
||||||
|
|
||||||
What should `type IntoIter` be set to?
|
What should `type IntoIter` be set to?\
|
||||||
Intuitively, it should be the type returned by `self.tickets.iter()`, i.e. the type returned by `Vec::iter()`.
|
Intuitively, it should be the type returned by `self.tickets.iter()`, i.e. the type returned by `Vec::iter()`.\
|
||||||
If you check the standard library documentation, you'll find that `Vec::iter()` returns an `std::slice::Iter`.
|
If you check the standard library documentation, you'll find that `Vec::iter()` returns an `std::slice::Iter`.
|
||||||
The definition of `Iter` is:
|
The definition of `Iter` is:
|
||||||
|
|
||||||
|
@ -30,7 +30,7 @@ pub struct Iter<'a, T> { /* fields omitted */ }
|
||||||
## Lifetime parameters
|
## Lifetime parameters
|
||||||
|
|
||||||
Lifetimes are **labels** used by the Rust compiler to keep track of how long a reference (either mutable or
|
Lifetimes are **labels** used by the Rust compiler to keep track of how long a reference (either mutable or
|
||||||
immutable) is valid.
|
immutable) is valid.\
|
||||||
The lifetime of a reference is constrained by the scope of the value it refers to. Rust always makes sure, at compile-time,
|
The lifetime of a reference is constrained by the scope of the value it refers to. Rust always makes sure, at compile-time,
|
||||||
that references are not used after the value they refer to has been dropped, to avoid dangling pointers and use-after-free bugs.
|
that references are not used after the value they refer to has been dropped, to avoid dangling pointers and use-after-free bugs.
|
||||||
|
|
||||||
|
@ -49,7 +49,7 @@ impl <T> Vec<T> {
|
||||||
}
|
}
|
||||||
```
|
```
|
||||||
|
|
||||||
`Vec::iter()` is generic over a lifetime parameter, named `'a`.
|
`Vec::iter()` is generic over a lifetime parameter, named `'a`.\
|
||||||
`'a` is used to **tie together** the lifetime of the `Vec` and the lifetime of the `Iter` returned by `iter()`.
|
`'a` is used to **tie together** the lifetime of the `Vec` and the lifetime of the `Iter` returned by `iter()`.
|
||||||
In plain English: the `Iter` returned by `iter()` cannot outlive the `Vec` reference (`&self`) it was created from.
|
In plain English: the `Iter` returned by `iter()` cannot outlive the `Vec` reference (`&self`) it was created from.
|
||||||
|
|
||||||
|
@ -74,7 +74,7 @@ No explicit lifetime parameter is present in the signature of `Vec::iter()`.
|
||||||
Elision rules imply that the lifetime of the `Iter` returned by `iter()` is tied to the lifetime of the `&self` reference.
|
Elision rules imply that the lifetime of the `Iter` returned by `iter()` is tied to the lifetime of the `&self` reference.
|
||||||
You can think of `'_` as a **placeholder** for the lifetime of the `&self` reference.
|
You can think of `'_` as a **placeholder** for the lifetime of the `&self` reference.
|
||||||
|
|
||||||
See the [References](#references) section for a link to the official documentation on lifetime elision.
|
See the [References](#references) section for a link to the official documentation on lifetime elision.\
|
||||||
In most cases, you can rely on the compiler telling you when you need to add explicit lifetime annotations.
|
In most cases, you can rely on the compiler telling you when you need to add explicit lifetime annotations.
|
||||||
|
|
||||||
## References
|
## References
|
||||||
|
|
|
@ -1,6 +1,6 @@
|
||||||
# Combinators
|
# Combinators
|
||||||
|
|
||||||
Iterators can do so much more than `for` loops!
|
Iterators can do so much more than `for` loops!\
|
||||||
If you look at the documentation for the `Iterator` trait, you'll find a **vast** collections of
|
If you look at the documentation for the `Iterator` trait, you'll find a **vast** collections of
|
||||||
methods that you can leverage to transform, filter, and combine iterators in various ways.
|
methods that you can leverage to transform, filter, and combine iterators in various ways.
|
||||||
|
|
||||||
|
@ -15,7 +15,7 @@ Let's mention the most common ones:
|
||||||
- `take` stops the iterator after `n` elements.
|
- `take` stops the iterator after `n` elements.
|
||||||
- `chain` combines two iterators into one.
|
- `chain` combines two iterators into one.
|
||||||
|
|
||||||
These methods are called **combinators**.
|
These methods are called **combinators**.\
|
||||||
They are usually **chained** together to create complex transformations in a concise and readable way:
|
They are usually **chained** together to create complex transformations in a concise and readable way:
|
||||||
|
|
||||||
```rust
|
```rust
|
||||||
|
@ -29,10 +29,10 @@ let outcome: u32 = numbers.iter()
|
||||||
|
|
||||||
## Closures
|
## Closures
|
||||||
|
|
||||||
What's going on with the `filter` and `map` methods above?
|
What's going on with the `filter` and `map` methods above?\
|
||||||
They take **closures** as arguments.
|
They take **closures** as arguments.
|
||||||
|
|
||||||
Closures are **anonymous functions**, i.e. functions that are not defined using the `fn` syntax we are used to.
|
Closures are **anonymous functions**, i.e. functions that are not defined using the `fn` syntax we are used to.\
|
||||||
They are defined using the `|args| body` syntax, where `args` are the arguments and `body` is the function body.
|
They are defined using the `|args| body` syntax, where `args` are the arguments and `body` is the function body.
|
||||||
`body` can be a block of code or a single expression.
|
`body` can be a block of code or a single expression.
|
||||||
For example:
|
For example:
|
||||||
|
@ -70,10 +70,10 @@ let add_one: fn(i32) -> i32 = |x| x + 1;
|
||||||
|
|
||||||
## `collect`
|
## `collect`
|
||||||
|
|
||||||
What happens when you're done transforming an iterator using combinators?
|
What happens when you're done transforming an iterator using combinators?\
|
||||||
You either iterate over the transformed values using a `for` loop, or you collect them into a collection.
|
You either iterate over the transformed values using a `for` loop, or you collect them into a collection.
|
||||||
|
|
||||||
The latter is done using the `collect` method.
|
The latter is done using the `collect` method.\
|
||||||
`collect` consumes the iterator and collects its elements into a collection of your choice.
|
`collect` consumes the iterator and collects its elements into a collection of your choice.
|
||||||
|
|
||||||
For example, you can collect the squares of the even numbers into a `Vec`:
|
For example, you can collect the squares of the even numbers into a `Vec`:
|
||||||
|
@ -86,7 +86,7 @@ let squares_of_evens: Vec<u32> = numbers.iter()
|
||||||
.collect();
|
.collect();
|
||||||
```
|
```
|
||||||
|
|
||||||
`collect` is generic over its **return type**.
|
`collect` is generic over its **return type**.\
|
||||||
Therefore you usually need to provide a type hint to help the compiler infer the correct type.
|
Therefore you usually need to provide a type hint to help the compiler infer the correct type.
|
||||||
In the example above, we annotated the type of `squares_of_evens` to be `Vec<u32>`.
|
In the example above, we annotated the type of `squares_of_evens` to be `Vec<u32>`.
|
||||||
Alternatively, you can use the **turbofish syntax** to specify the type:
|
Alternatively, you can use the **turbofish syntax** to specify the type:
|
||||||
|
|
|
@ -1,6 +1,6 @@
|
||||||
# `impl Trait`
|
# `impl Trait`
|
||||||
|
|
||||||
`TicketStore::to_dos` returns a `Vec<&Ticket>`.
|
`TicketStore::to_dos` returns a `Vec<&Ticket>`.\
|
||||||
That signature introduces a new heap allocation every time `to_dos` is called, which may be unnecessary depending
|
That signature introduces a new heap allocation every time `to_dos` is called, which may be unnecessary depending
|
||||||
on what the caller needs to do with the result.
|
on what the caller needs to do with the result.
|
||||||
It'd be better if `to_dos` returned an iterator instead of a `Vec`, thus empowering the caller to decide whether to
|
It'd be better if `to_dos` returned an iterator instead of a `Vec`, thus empowering the caller to decide whether to
|
||||||
|
@ -25,8 +25,8 @@ The `filter` method returns an instance of `std::iter::Filter`, which has the fo
|
||||||
pub struct Filter<I, P> { /* fields omitted */ }
|
pub struct Filter<I, P> { /* fields omitted */ }
|
||||||
```
|
```
|
||||||
|
|
||||||
where `I` is the type of the iterator being filtered on and `P` is the predicate used to filter the elements.
|
where `I` is the type of the iterator being filtered on and `P` is the predicate used to filter the elements.\
|
||||||
We know that `I` is `std::slice::Iter<'_, Ticket>` in this case, but what about `P`?
|
We know that `I` is `std::slice::Iter<'_, Ticket>` in this case, but what about `P`?\
|
||||||
`P` is a closure, an **anonymous function**. As the name suggests, closures don't have a name,
|
`P` is a closure, an **anonymous function**. As the name suggests, closures don't have a name,
|
||||||
so we can't write them down in our code.
|
so we can't write them down in our code.
|
||||||
|
|
||||||
|
@ -65,5 +65,5 @@ only that it implements the specified trait(s). But the compiler knows the exact
|
||||||
|
|
||||||
## RPIT
|
## RPIT
|
||||||
|
|
||||||
If you read RFCs or deep-dives about Rust, you might come across the acronym **RPIT**.
|
If you read RFCs or deep-dives about Rust, you might come across the acronym **RPIT**.\
|
||||||
It stands for **"Return Position Impl Trait"** and refers to the use of `impl Trait` in return position.
|
It stands for **"Return Position Impl Trait"** and refers to the use of `impl Trait` in return position.
|
|
@ -1,6 +1,6 @@
|
||||||
# `impl Trait` in argument position
|
# `impl Trait` in argument position
|
||||||
|
|
||||||
In the previous section, we saw how `impl Trait` can be used to return a type without specifying its name.
|
In the previous section, we saw how `impl Trait` can be used to return a type without specifying its name.\
|
||||||
The same syntax can also be used in **argument position**:
|
The same syntax can also be used in **argument position**:
|
||||||
|
|
||||||
```rust
|
```rust
|
||||||
|
@ -11,7 +11,7 @@ fn print_iter(iter: impl Iterator<Item = i32>) {
|
||||||
}
|
}
|
||||||
```
|
```
|
||||||
|
|
||||||
`print_iter` takes an iterator of `i32`s and prints each element.
|
`print_iter` takes an iterator of `i32`s and prints each element.\
|
||||||
When used in **argument position**, `impl Trait` is equivalent to a generic parameter with a trait bound:
|
When used in **argument position**, `impl Trait` is equivalent to a generic parameter with a trait bound:
|
||||||
|
|
||||||
```rust
|
```rust
|
||||||
|
@ -27,6 +27,6 @@ where
|
||||||
|
|
||||||
## Downsides
|
## Downsides
|
||||||
|
|
||||||
As a rule of thumb, prefer generics over `impl Trait` in argument position.
|
As a rule of thumb, prefer generics over `impl Trait` in argument position.\
|
||||||
Generics allow the caller to explicitly specify the type of the argument, using the turbofish syntax (`::<>`),
|
Generics allow the caller to explicitly specify the type of the argument, using the turbofish syntax (`::<>`),
|
||||||
which can be useful for disambiguation. That's not the case with `impl Trait`.
|
which can be useful for disambiguation. That's not the case with `impl Trait`.
|
|
@ -21,12 +21,12 @@ Heap: | 1 | 2 | ? |
|
||||||
+---+---+---+
|
+---+---+---+
|
||||||
```
|
```
|
||||||
|
|
||||||
We already remarked how `String` is just a `Vec<u8>` in disguise.
|
We already remarked how `String` is just a `Vec<u8>` in disguise.\
|
||||||
The similarity should prompt you to ask: "What's the equivalent of `&str` for `Vec`?"
|
The similarity should prompt you to ask: "What's the equivalent of `&str` for `Vec`?"
|
||||||
|
|
||||||
## `&[T]`
|
## `&[T]`
|
||||||
|
|
||||||
`[T]` is a **slice** of a contiguous sequence of elements of type `T`.
|
`[T]` is a **slice** of a contiguous sequence of elements of type `T`.\
|
||||||
It's most commonly used in its borrowed form, `&[T]`.
|
It's most commonly used in its borrowed form, `&[T]`.
|
||||||
|
|
||||||
There are various ways to create a slice reference from a `Vec`:
|
There are various ways to create a slice reference from a `Vec`:
|
||||||
|
@ -54,7 +54,7 @@ let sum: i32 = numbers.iter().sum();
|
||||||
|
|
||||||
### Memory layout
|
### Memory layout
|
||||||
|
|
||||||
A `&[T]` is a **fat pointer**, just like `&str`.
|
A `&[T]` is a **fat pointer**, just like `&str`.\
|
||||||
It consists of a pointer to the first element of the slice and the length of the slice.
|
It consists of a pointer to the first element of the slice and the length of the slice.
|
||||||
|
|
||||||
If you have a `Vec` with three elements:
|
If you have a `Vec` with three elements:
|
||||||
|
@ -90,7 +90,7 @@ Heap: | 1 | 2 | 3 | ? | |
|
||||||
|
|
||||||
### `&Vec<T>` vs `&[T]`
|
### `&Vec<T>` vs `&[T]`
|
||||||
|
|
||||||
When you need to pass an immutable reference to a `Vec` to a function, prefer `&[T]` over `&Vec<T>`.
|
When you need to pass an immutable reference to a `Vec` to a function, prefer `&[T]` over `&Vec<T>`.\
|
||||||
This allows the function to accept any kind of slice, not necessarily one backed by a `Vec`.
|
This allows the function to accept any kind of slice, not necessarily one backed by a `Vec`.
|
||||||
|
|
||||||
For example, you can then pass a subset of the elements in a `Vec`.
|
For example, you can then pass a subset of the elements in a `Vec`.
|
||||||
|
|
|
@ -1,6 +1,6 @@
|
||||||
# Mutable slices
|
# Mutable slices
|
||||||
|
|
||||||
Every time we've talked about slice types (like `str` and `[T]`), we've used their immutable borrow form (`&str` and `&[T]`).
|
Every time we've talked about slice types (like `str` and `[T]`), we've used their immutable borrow form (`&str` and `&[T]`).\
|
||||||
But slices can also be mutable!
|
But slices can also be mutable!
|
||||||
|
|
||||||
Here's how you create a mutable slice:
|
Here's how you create a mutable slice:
|
||||||
|
@ -21,7 +21,7 @@ This will change the first element of the `Vec` to `42`.
|
||||||
## Limitations
|
## Limitations
|
||||||
|
|
||||||
When working with immutable borrows, the recommendation was clear: prefer slice references over references to
|
When working with immutable borrows, the recommendation was clear: prefer slice references over references to
|
||||||
the owned type (e.g. `&[T]` over `&Vec<T>`).
|
the owned type (e.g. `&[T]` over `&Vec<T>`).\
|
||||||
That's **not** the case with mutable borrows.
|
That's **not** the case with mutable borrows.
|
||||||
|
|
||||||
Consider this scenario:
|
Consider this scenario:
|
||||||
|
@ -32,10 +32,10 @@ let mut slice: &mut [i32] = &mut numbers;
|
||||||
slice.push(1);
|
slice.push(1);
|
||||||
```
|
```
|
||||||
|
|
||||||
It won't compile!
|
It won't compile!\
|
||||||
`push` is a method on `Vec`, not on slices. This is the manifestation of a more general principle: Rust won't
|
`push` is a method on `Vec`, not on slices. This is the manifestation of a more general principle: Rust won't
|
||||||
allow you to add or remove elements from a slice. You will only be able to modify/replace the elements that are
|
allow you to add or remove elements from a slice. You will only be able to modify/replace the elements that are
|
||||||
already there.
|
already there.
|
||||||
|
|
||||||
In this regard, a `&mut Vec` or a `&mut String` are strictly more powerful than a `&mut [T]` or a `&mut str`.
|
In this regard, a `&mut Vec` or a `&mut String` are strictly more powerful than a `&mut [T]` or a `&mut str`.\
|
||||||
Choose the type that best fits based on the operations you need to perform.
|
Choose the type that best fits based on the operations you need to perform.
|
|
@ -1,6 +1,6 @@
|
||||||
# Ticket ids
|
# Ticket ids
|
||||||
|
|
||||||
Let's think again about our ticket management system.
|
Let's think again about our ticket management system.\
|
||||||
Our ticket model right now looks like this:
|
Our ticket model right now looks like this:
|
||||||
|
|
||||||
```rust
|
```rust
|
||||||
|
@ -11,13 +11,13 @@ pub struct Ticket {
|
||||||
}
|
}
|
||||||
```
|
```
|
||||||
|
|
||||||
One thing is missing here: an **identifier** to uniquely identify a ticket.
|
One thing is missing here: an **identifier** to uniquely identify a ticket.\
|
||||||
That identifier should be unique for each ticket. That can be guaranteed by generating it automatically when
|
That identifier should be unique for each ticket. That can be guaranteed by generating it automatically when
|
||||||
a new ticket is created.
|
a new ticket is created.
|
||||||
|
|
||||||
## Refining the model
|
## Refining the model
|
||||||
|
|
||||||
Where should the id be stored?
|
Where should the id be stored?\
|
||||||
We could add a new field to the `Ticket` struct:
|
We could add a new field to the `Ticket` struct:
|
||||||
|
|
||||||
```rust
|
```rust
|
||||||
|
@ -29,7 +29,7 @@ pub struct Ticket {
|
||||||
}
|
}
|
||||||
```
|
```
|
||||||
|
|
||||||
But we don't know the id before creating the ticket. So it can't be there from the get-go.
|
But we don't know the id before creating the ticket. So it can't be there from the get-go.\
|
||||||
It'd have to be optional:
|
It'd have to be optional:
|
||||||
|
|
||||||
```rust
|
```rust
|
||||||
|
@ -61,7 +61,7 @@ pub struct Ticket {
|
||||||
}
|
}
|
||||||
```
|
```
|
||||||
|
|
||||||
A `TicketDraft` is a ticket that hasn't been created yet. It doesn't have an id, and it doesn't have a status.
|
A `TicketDraft` is a ticket that hasn't been created yet. It doesn't have an id, and it doesn't have a status.\
|
||||||
A `Ticket` is a ticket that has been created. It has an id and a status.
|
A `Ticket` is a ticket that has been created. It has an id and a status.\
|
||||||
Since each field in `TicketDraft` and `Ticket` embeds its own constraints, we don't have to duplicate logic
|
Since each field in `TicketDraft` and `Ticket` embeds its own constraints, we don't have to duplicate logic
|
||||||
across the two types.
|
across the two types.
|
|
@ -1,6 +1,6 @@
|
||||||
# Indexing
|
# Indexing
|
||||||
|
|
||||||
`TicketStore::get` returns an `Option<&Ticket>` for a given `TicketId`.
|
`TicketStore::get` returns an `Option<&Ticket>` for a given `TicketId`.\
|
||||||
We've seen before how to access elements of arrays and vectors using Rust's
|
We've seen before how to access elements of arrays and vectors using Rust's
|
||||||
indexing syntax:
|
indexing syntax:
|
||||||
|
|
||||||
|
@ -9,7 +9,7 @@ let v = vec![0, 1, 2];
|
||||||
assert_eq!(v[0], 0);
|
assert_eq!(v[0], 0);
|
||||||
```
|
```
|
||||||
|
|
||||||
How can we provide the same experience for `TicketStore`?
|
How can we provide the same experience for `TicketStore`?\
|
||||||
You guessed right: we need to implement a trait, `Index`!
|
You guessed right: we need to implement a trait, `Index`!
|
||||||
|
|
||||||
## `Index`
|
## `Index`
|
||||||
|
|
|
@ -42,13 +42,13 @@ where
|
||||||
}
|
}
|
||||||
```
|
```
|
||||||
|
|
||||||
The key type must implement the `Eq` and `Hash` traits.
|
The key type must implement the `Eq` and `Hash` traits.\
|
||||||
Let's dig into those two.
|
Let's dig into those two.
|
||||||
|
|
||||||
## `Hash`
|
## `Hash`
|
||||||
|
|
||||||
A hashing function (or hasher) maps a potentially infinite set of a values (e.g.
|
A hashing function (or hasher) maps a potentially infinite set of a values (e.g.
|
||||||
all possible strings) to a bounded range (e.g. a `u64` value).
|
all possible strings) to a bounded range (e.g. a `u64` value).\
|
||||||
There are many different hashing functions around, each with different properties
|
There are many different hashing functions around, each with different properties
|
||||||
(speed, collision risk, reversibility, etc.).
|
(speed, collision risk, reversibility, etc.).
|
||||||
|
|
||||||
|
@ -81,10 +81,10 @@ struct Person {
|
||||||
`HashMap` must be able to compare keys for equality. This is particularly important
|
`HashMap` must be able to compare keys for equality. This is particularly important
|
||||||
when dealing with hash collisions—i.e. when two different keys hash to the same value.
|
when dealing with hash collisions—i.e. when two different keys hash to the same value.
|
||||||
|
|
||||||
You may wonder: isn't that what the `PartialEq` trait is for? Almost!
|
You may wonder: isn't that what the `PartialEq` trait is for? Almost!\
|
||||||
`PartialEq` is not enough for `HashMap` because it doesn't guarantee reflexivity, i.e. `a == a` is always `true`.
|
`PartialEq` is not enough for `HashMap` because it doesn't guarantee reflexivity, i.e. `a == a` is always `true`.\
|
||||||
For example, floating point numbers (`f32` and `f64`) implement `PartialEq`,
|
For example, floating point numbers (`f32` and `f64`) implement `PartialEq`,
|
||||||
but they don't satisfy the reflexivity property: `f32::NAN == f32::NAN` is `false`.
|
but they don't satisfy the reflexivity property: `f32::NAN == f32::NAN` is `false`.\
|
||||||
Reflexivity is crucial for `HashMap` to work correctly: without it, you wouldn't be able to retrieve a value
|
Reflexivity is crucial for `HashMap` to work correctly: without it, you wouldn't be able to retrieve a value
|
||||||
from the map using the same key you used to insert it.
|
from the map using the same key you used to insert it.
|
||||||
|
|
||||||
|
|
|
@ -1,16 +1,16 @@
|
||||||
# Ordering
|
# Ordering
|
||||||
|
|
||||||
By moving from a `Vec` to a `HashMap` we have improved the performance of our ticket management system,
|
By moving from a `Vec` to a `HashMap` we have improved the performance of our ticket management system,
|
||||||
and simplified our code in the process.
|
and simplified our code in the process.\
|
||||||
It's not all roses, though. When iterating over a `Vec`-backed store, we could be sure that the tickets
|
It's not all roses, though. When iterating over a `Vec`-backed store, we could be sure that the tickets
|
||||||
would be returned in the order they were added.
|
would be returned in the order they were added.\
|
||||||
That's not the case with a `HashMap`: you can iterate over the tickets, but the order is random.
|
That's not the case with a `HashMap`: you can iterate over the tickets, but the order is random.
|
||||||
|
|
||||||
We can recover a consistent ordering by switching from a `HashMap` to a `BTreeMap`.
|
We can recover a consistent ordering by switching from a `HashMap` to a `BTreeMap`.
|
||||||
|
|
||||||
## `BTreeMap`
|
## `BTreeMap`
|
||||||
|
|
||||||
A `BTreeMap` guarantees that entries are sorted by their keys.
|
A `BTreeMap` guarantees that entries are sorted by their keys.\
|
||||||
This is useful when you need to iterate over the entries in a specific order, or if you need to
|
This is useful when you need to iterate over the entries in a specific order, or if you need to
|
||||||
perform range queries (e.g. "give me all tickets with an id between 10 and 20").
|
perform range queries (e.g. "give me all tickets with an id between 10 and 20").
|
||||||
|
|
||||||
|
@ -34,7 +34,7 @@ impl<K, V> BTreeMap<K, V> {
|
||||||
|
|
||||||
## `Ord`
|
## `Ord`
|
||||||
|
|
||||||
The `Ord` trait is used to compare values.
|
The `Ord` trait is used to compare values.\
|
||||||
While `PartialEq` is used to compare for equality, `Ord` is used to compare for ordering.
|
While `PartialEq` is used to compare for equality, `Ord` is used to compare for ordering.
|
||||||
|
|
||||||
It's defined in `std::cmp`:
|
It's defined in `std::cmp`:
|
||||||
|
@ -46,7 +46,7 @@ pub trait Ord: Eq + PartialOrd {
|
||||||
```
|
```
|
||||||
|
|
||||||
The `cmp` method returns an `Ordering` enum, which can be one
|
The `cmp` method returns an `Ordering` enum, which can be one
|
||||||
of `Less`, `Equal`, or `Greater`.
|
of `Less`, `Equal`, or `Greater`.\
|
||||||
`Ord` requires that two other traits are implemented: `Eq` and `PartialOrd`.
|
`Ord` requires that two other traits are implemented: `Eq` and `PartialOrd`.
|
||||||
|
|
||||||
## `PartialOrd`
|
## `PartialOrd`
|
||||||
|
@ -61,7 +61,7 @@ pub trait PartialOrd: PartialEq {
|
||||||
```
|
```
|
||||||
|
|
||||||
`PartialOrd::partial_cmp` returns an `Option`—it is not guaranteed that two values can
|
`PartialOrd::partial_cmp` returns an `Option`—it is not guaranteed that two values can
|
||||||
be compared.
|
be compared.\
|
||||||
For example, `f32` doesn't implement `Ord` because `NaN` values are not comparable,
|
For example, `f32` doesn't implement `Ord` because `NaN` values are not comparable,
|
||||||
the same reason why `f32` doesn't implement `Eq`.
|
the same reason why `f32` doesn't implement `Eq`.
|
||||||
|
|
||||||
|
|
|
@ -1,10 +1,10 @@
|
||||||
# Intro
|
# Intro
|
||||||
|
|
||||||
One of Rust's big promises is *fearless concurrency*: making it easier to write safe, concurrent programs.
|
One of Rust's big promises is _fearless concurrency_: making it easier to write safe, concurrent programs.
|
||||||
We haven't seen much of that yet. All the work we've done so far has been single-threaded.
|
We haven't seen much of that yet. All the work we've done so far has been single-threaded.
|
||||||
Time to change that!
|
Time to change that!
|
||||||
|
|
||||||
In this chapter we'll make our ticket store multithreaded.
|
In this chapter we'll make our ticket store multithreaded.\
|
||||||
We'll have the opportunity to touch most of Rust's core concurrency features, including:
|
We'll have the opportunity to touch most of Rust's core concurrency features, including:
|
||||||
|
|
||||||
- Threads, using the `std::thread` module
|
- Threads, using the `std::thread` module
|
||||||
|
|
|
@ -5,21 +5,21 @@ and why we might want to use them.
|
||||||
|
|
||||||
## What is a thread?
|
## What is a thread?
|
||||||
|
|
||||||
A **thread** is an execution context managed by the underlying operating system.
|
A **thread** is an execution context managed by the underlying operating system.\
|
||||||
Each thread has its own stack, instruction pointer, and program counter.
|
Each thread has its own stack, instruction pointer, and program counter.
|
||||||
|
|
||||||
A single **process** can manage multiple threads.
|
A single **process** can manage multiple threads.
|
||||||
These threads share the same memory space, which means they can access the same data.
|
These threads share the same memory space, which means they can access the same data.
|
||||||
|
|
||||||
Threads are a **logical** construct. In the end, you can only run one set of instructions
|
Threads are a **logical** construct. In the end, you can only run one set of instructions
|
||||||
at a time on a CPU core, the **physical** execution unit.
|
at a time on a CPU core, the **physical** execution unit.\
|
||||||
Since there can be many more threads than there are CPU cores, the operating system's
|
Since there can be many more threads than there are CPU cores, the operating system's
|
||||||
**scheduler** is in charge of deciding which thread to run at any given time,
|
**scheduler** is in charge of deciding which thread to run at any given time,
|
||||||
partitioning CPU time among them to maximize throughput and responsiveness.
|
partitioning CPU time among them to maximize throughput and responsiveness.
|
||||||
|
|
||||||
## `main`
|
## `main`
|
||||||
|
|
||||||
When a Rust program starts, it runs on a single thread, the **main thread**.
|
When a Rust program starts, it runs on a single thread, the **main thread**.\
|
||||||
This thread is created by the operating system and is responsible for running the `main`
|
This thread is created by the operating system and is responsible for running the `main`
|
||||||
function.
|
function.
|
||||||
|
|
||||||
|
@ -66,12 +66,12 @@ fn main() {
|
||||||
```
|
```
|
||||||
|
|
||||||
If you execute this program on the [Rust playground](https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=afedf7062298ca8f5a248bc551062eaa)
|
If you execute this program on the [Rust playground](https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=afedf7062298ca8f5a248bc551062eaa)
|
||||||
you'll see that the main thread and the spawned thread run concurrently.
|
you'll see that the main thread and the spawned thread run concurrently.\
|
||||||
Each thread makes progress independently of the other.
|
Each thread makes progress independently of the other.
|
||||||
|
|
||||||
### Process termination
|
### Process termination
|
||||||
|
|
||||||
When the main thread finishes, the overall process will exit.
|
When the main thread finishes, the overall process will exit.\
|
||||||
A spawned thread will continue running until it finishes or the main thread finishes.
|
A spawned thread will continue running until it finishes or the main thread finishes.
|
||||||
|
|
||||||
```rust
|
```rust
|
||||||
|
@ -90,7 +90,7 @@ fn main() {
|
||||||
}
|
}
|
||||||
```
|
```
|
||||||
|
|
||||||
In the example above, you can expect to see the message "Hello from a thread!" printed roughly five times.
|
In the example above, you can expect to see the message "Hello from a thread!" printed roughly five times.\
|
||||||
Then the main thread will finish (when the `sleep` call returns), and the spawned thread will be terminated
|
Then the main thread will finish (when the `sleep` call returns), and the spawned thread will be terminated
|
||||||
since the overall process exits.
|
since the overall process exits.
|
||||||
|
|
||||||
|
@ -109,7 +109,7 @@ fn main() {
|
||||||
}
|
}
|
||||||
```
|
```
|
||||||
|
|
||||||
In this example, the main thread will wait for the spawned thread to finish before exiting.
|
In this example, the main thread will wait for the spawned thread to finish before exiting.\
|
||||||
This introduces a form of **synchronization** between the two threads: you're guaranteed to see the message
|
This introduces a form of **synchronization** between the two threads: you're guaranteed to see the message
|
||||||
"Hello from a thread!" printed before the program exits, because the main thread won't exit
|
"Hello from a thread!" printed before the program exits, because the main thread won't exit
|
||||||
until the spawned thread has finished.
|
until the spawned thread has finished.
|
||||||
|
|
|
@ -20,12 +20,12 @@ error[E0597]: `v` does not live long enough
|
||||||
|
|
||||||
`argument requires that v is borrowed for 'static`, what does that mean?
|
`argument requires that v is borrowed for 'static`, what does that mean?
|
||||||
|
|
||||||
The `'static` lifetime is a special lifetime in Rust.
|
The `'static` lifetime is a special lifetime in Rust.\
|
||||||
It means that the value will be valid for the entire duration of the program.
|
It means that the value will be valid for the entire duration of the program.
|
||||||
|
|
||||||
## Detached threads
|
## Detached threads
|
||||||
|
|
||||||
A thread launched via `thread::spawn` can **outlive** the thread that spawned it.
|
A thread launched via `thread::spawn` can **outlive** the thread that spawned it.\
|
||||||
For example:
|
For example:
|
||||||
|
|
||||||
```rust
|
```rust
|
||||||
|
@ -44,10 +44,10 @@ fn f() {
|
||||||
```
|
```
|
||||||
|
|
||||||
In this example, the first spawned thread will in turn spawn
|
In this example, the first spawned thread will in turn spawn
|
||||||
a child thread that prints a message every second.
|
a child thread that prints a message every second.\
|
||||||
The first thread will then finish and exit. When that happens,
|
The first thread will then finish and exit. When that happens,
|
||||||
its child thread will **continue running** for as long as the
|
its child thread will **continue running** for as long as the
|
||||||
overall process is running.
|
overall process is running.\
|
||||||
In Rust's lingo, we say that the child thread has **outlived**
|
In Rust's lingo, we say that the child thread has **outlived**
|
||||||
its parent.
|
its parent.
|
||||||
|
|
||||||
|
@ -59,7 +59,7 @@ Since a spawned thread can:
|
||||||
- run until the program exits
|
- run until the program exits
|
||||||
|
|
||||||
it must not borrow any values that might be dropped before the program exits;
|
it must not borrow any values that might be dropped before the program exits;
|
||||||
violating this constraint would expose us to a use-after-free bug.
|
violating this constraint would expose us to a use-after-free bug.\
|
||||||
That's why `std::thread::spawn`'s signature requires that the closure passed to it
|
That's why `std::thread::spawn`'s signature requires that the closure passed to it
|
||||||
has the `'static` lifetime:
|
has the `'static` lifetime:
|
||||||
|
|
||||||
|
@ -104,7 +104,7 @@ The most common case is a reference to **static data**, such as string literals:
|
||||||
let s: &'static str = "Hello world!";
|
let s: &'static str = "Hello world!";
|
||||||
```
|
```
|
||||||
|
|
||||||
Since string literals are known at compile-time, Rust stores them *inside* your executable,
|
Since string literals are known at compile-time, Rust stores them _inside_ your executable,
|
||||||
in a region known as **read-only data segment**.
|
in a region known as **read-only data segment**.
|
||||||
All references pointing to that region will therefore be valid for as long as
|
All references pointing to that region will therefore be valid for as long as
|
||||||
the program runs; they satisfy the `'static` contract.
|
the program runs; they satisfy the `'static` contract.
|
||||||
|
|
|
@ -1,7 +1,7 @@
|
||||||
# Leaking data
|
# Leaking data
|
||||||
|
|
||||||
The main concern around passing references to spawned threads is use-after-free bugs:
|
The main concern around passing references to spawned threads is use-after-free bugs:
|
||||||
accessing data using a pointer to a memory region that's already been freed/de-allocated.
|
accessing data using a pointer to a memory region that's already been freed/de-allocated.\
|
||||||
If you're working with heap-allocated data, you can avoid the issue by
|
If you're working with heap-allocated data, you can avoid the issue by
|
||||||
telling Rust that you'll never reclaim that memory: you choose to **leak memory**,
|
telling Rust that you'll never reclaim that memory: you choose to **leak memory**,
|
||||||
intentionally.
|
intentionally.
|
||||||
|
@ -32,7 +32,7 @@ fn oom_trigger() {
|
||||||
}
|
}
|
||||||
```
|
```
|
||||||
|
|
||||||
At the same time, memory leaked via `Box::leak` is not truly forgotten.
|
At the same time, memory leaked via `Box::leak` is not truly forgotten.\
|
||||||
The operating system can map each memory region to the process responsible for it.
|
The operating system can map each memory region to the process responsible for it.
|
||||||
When the process exits, the operating system will reclaim that memory.
|
When the process exits, the operating system will reclaim that memory.
|
||||||
|
|
||||||
|
|
|
@ -1,7 +1,7 @@
|
||||||
# Scoped threads
|
# Scoped threads
|
||||||
|
|
||||||
All the lifetime issues we discussed so far have a common source:
|
All the lifetime issues we discussed so far have a common source:
|
||||||
the spawned thread can outlive its parent.
|
the spawned thread can outlive its parent.\
|
||||||
We can sidestep this issue by using **scoped threads**.
|
We can sidestep this issue by using **scoped threads**.
|
||||||
|
|
||||||
```rust
|
```rust
|
||||||
|
@ -26,12 +26,12 @@ Let's unpack what's happening.
|
||||||
|
|
||||||
## `scope`
|
## `scope`
|
||||||
|
|
||||||
The `std::thread::scope` function creates a new **scope**.
|
The `std::thread::scope` function creates a new **scope**.\
|
||||||
`std::thread::scope` takes as input a closure, with a single argument: a `Scope` instance.
|
`std::thread::scope` takes as input a closure, with a single argument: a `Scope` instance.
|
||||||
|
|
||||||
## Scoped spawns
|
## Scoped spawns
|
||||||
|
|
||||||
`Scope` exposes a `spawn` method.
|
`Scope` exposes a `spawn` method.\
|
||||||
Unlike `std::thread::spawn`, all threads spawned using a `Scope` will be
|
Unlike `std::thread::spawn`, all threads spawned using a `Scope` will be
|
||||||
**automatically joined** when the scope ends.
|
**automatically joined** when the scope ends.
|
||||||
|
|
||||||
|
|
|
@ -1,6 +1,6 @@
|
||||||
# Channels
|
# Channels
|
||||||
|
|
||||||
All our spawned threads have been fairly short-lived so far.
|
All our spawned threads have been fairly short-lived so far.\
|
||||||
Get some input, run a computation, return the result, shut down.
|
Get some input, run a computation, return the result, shut down.
|
||||||
|
|
||||||
For our ticket management system, we want to do something different:
|
For our ticket management system, we want to do something different:
|
||||||
|
@ -9,10 +9,10 @@ a client-server architecture.
|
||||||
We will have **one long-running server thread**, responsible for managing
|
We will have **one long-running server thread**, responsible for managing
|
||||||
our state, the stored tickets.
|
our state, the stored tickets.
|
||||||
|
|
||||||
We will then have **multiple client threads**.
|
We will then have **multiple client threads**.\
|
||||||
Each client will be able to send **commands** and **queries** to
|
Each client will be able to send **commands** and **queries** to
|
||||||
the stateful thread, in order to change its state (e.g. add a new ticket)
|
the stateful thread, in order to change its state (e.g. add a new ticket)
|
||||||
or retrieve information (e.g. get the status of a ticket).
|
or retrieve information (e.g. get the status of a ticket).\
|
||||||
Client threads will run concurrently.
|
Client threads will run concurrently.
|
||||||
|
|
||||||
## Communication
|
## Communication
|
||||||
|
@ -22,7 +22,7 @@ So far we've only had very limited parent-child communication:
|
||||||
- The spawned thread borrowed/consumed data from the parent context
|
- The spawned thread borrowed/consumed data from the parent context
|
||||||
- The spawned thread returned data to the parent when joined
|
- The spawned thread returned data to the parent when joined
|
||||||
|
|
||||||
This isn't enough for a client-server design.
|
This isn't enough for a client-server design.\
|
||||||
Clients need to be able to send and receive data from the server thread
|
Clients need to be able to send and receive data from the server thread
|
||||||
_after_ it has been launched.
|
_after_ it has been launched.
|
||||||
|
|
||||||
|
@ -31,7 +31,7 @@ We can solve the issue using **channels**.
|
||||||
## Channels
|
## Channels
|
||||||
|
|
||||||
Rust's standard library provides **multi-producer, single-consumer** (mpsc) channels
|
Rust's standard library provides **multi-producer, single-consumer** (mpsc) channels
|
||||||
in its `std::sync::mpsc` module.
|
in its `std::sync::mpsc` module.\
|
||||||
There are two channel flavours: bounded and unbounded. We'll stick to the unbounded
|
There are two channel flavours: bounded and unbounded. We'll stick to the unbounded
|
||||||
version for now, but we'll discuss the pros and cons later on.
|
version for now, but we'll discuss the pros and cons later on.
|
||||||
|
|
||||||
|
@ -43,8 +43,8 @@ use std::sync::mpsc::channel;
|
||||||
let (sender, receiver) = channel();
|
let (sender, receiver) = channel();
|
||||||
```
|
```
|
||||||
|
|
||||||
You get a sender and a receiver.
|
You get a sender and a receiver.\
|
||||||
You call `send` on the sender to push data into the channel.
|
You call `send` on the sender to push data into the channel.\
|
||||||
You call `recv` on the receiver to pull data from the channel.
|
You call `recv` on the receiver to pull data from the channel.
|
||||||
|
|
||||||
### Multiple senders
|
### Multiple senders
|
||||||
|
@ -59,15 +59,15 @@ That's what **mpsc** (multi-producer single-consumer) stands for!
|
||||||
|
|
||||||
### Message type
|
### Message type
|
||||||
|
|
||||||
Both `Sender` and `Receiver` are generic over a type parameter `T`.
|
Both `Sender` and `Receiver` are generic over a type parameter `T`.\
|
||||||
That's the type of the _messages_ that can travel on our channel.
|
That's the type of the _messages_ that can travel on our channel.
|
||||||
|
|
||||||
It could be a `u64`, a struct, an enum, etc.
|
It could be a `u64`, a struct, an enum, etc.
|
||||||
|
|
||||||
### Errors
|
### Errors
|
||||||
|
|
||||||
Both `send` and `recv` can fail.
|
Both `send` and `recv` can fail.\
|
||||||
`send` returns an error if the receiver has been dropped.
|
`send` returns an error if the receiver has been dropped.\
|
||||||
`recv` returns an error if all senders have been dropped and the channel is empty.
|
`recv` returns an error if all senders have been dropped and the channel is empty.
|
||||||
|
|
||||||
In other words, `send` and `recv` error when the channel is effectively closed.
|
In other words, `send` and `recv` error when the channel is effectively closed.
|
|
@ -10,7 +10,7 @@ impl<T> Sender<T> {
|
||||||
}
|
}
|
||||||
```
|
```
|
||||||
|
|
||||||
`send` takes `&self` as its argument.
|
`send` takes `&self` as its argument.\
|
||||||
But it's clearly causing a mutation: it's adding a new message to the channel.
|
But it's clearly causing a mutation: it's adding a new message to the channel.
|
||||||
What's even more interesting is that `Sender` is cloneable: we can have multiple instances of `Sender`
|
What's even more interesting is that `Sender` is cloneable: we can have multiple instances of `Sender`
|
||||||
trying to modify the channel state **at the same time**, from different threads.
|
trying to modify the channel state **at the same time**, from different threads.
|
||||||
|
@ -32,7 +32,7 @@ It would have been more accurate to name them:
|
||||||
|
|
||||||
Immutable/mutable is a mental model that works for the vast majority of cases, and it's a great one to get started
|
Immutable/mutable is a mental model that works for the vast majority of cases, and it's a great one to get started
|
||||||
with Rust. But it's not the whole story, as you've just seen: `&T` doesn't actually guarantee that the data it
|
with Rust. But it's not the whole story, as you've just seen: `&T` doesn't actually guarantee that the data it
|
||||||
points to is immutable.
|
points to is immutable.\
|
||||||
Don't worry, though: Rust is still keeping its promises.
|
Don't worry, though: Rust is still keeping its promises.
|
||||||
It's just that the terms are a bit more nuanced than they might seem at first.
|
It's just that the terms are a bit more nuanced than they might seem at first.
|
||||||
|
|
||||||
|
@ -40,15 +40,15 @@ It's just that the terms are a bit more nuanced than they might seem at first.
|
||||||
|
|
||||||
Whenever a type allows you to mutate data through a shared reference, you're dealing with **interior mutability**.
|
Whenever a type allows you to mutate data through a shared reference, you're dealing with **interior mutability**.
|
||||||
|
|
||||||
By default, the Rust compiler assumes that shared references are immutable. It **optimises your code** based on that assumption.
|
By default, the Rust compiler assumes that shared references are immutable. It **optimises your code** based on that assumption.\
|
||||||
The compiler can reorder operations, cache values, and do all sorts of magic to make your code faster.
|
The compiler can reorder operations, cache values, and do all sorts of magic to make your code faster.
|
||||||
|
|
||||||
You can tell the compiler "No, this shared reference is actually mutable" by wrapping the data in an `UnsafeCell`.
|
You can tell the compiler "No, this shared reference is actually mutable" by wrapping the data in an `UnsafeCell`.\
|
||||||
Every time you see a type that allows interior mutability, you can be certain that `UnsafeCell` is involved,
|
Every time you see a type that allows interior mutability, you can be certain that `UnsafeCell` is involved,
|
||||||
either directly or indirectly.
|
either directly or indirectly.\
|
||||||
Using `UnsafeCell`, raw pointers and `unsafe` code, you can mutate data through shared references.
|
Using `UnsafeCell`, raw pointers and `unsafe` code, you can mutate data through shared references.
|
||||||
|
|
||||||
Let's be clear, though: `UnsafeCell` isn't a magic wand that allows you to ignore the borrow-checker!
|
Let's be clear, though: `UnsafeCell` isn't a magic wand that allows you to ignore the borrow-checker!\
|
||||||
`unsafe` code is still subject to Rust's rules about borrowing and aliasing.
|
`unsafe` code is still subject to Rust's rules about borrowing and aliasing.
|
||||||
It's an (advanced) tool that you can leverage to build **safe abstractions** whose safety can't be directly expressed
|
It's an (advanced) tool that you can leverage to build **safe abstractions** whose safety can't be directly expressed
|
||||||
in Rust's type system. Whenever you use the `unsafe` keyword you're telling the compiler:
|
in Rust's type system. Whenever you use the `unsafe` keyword you're telling the compiler:
|
||||||
|
@ -64,15 +64,15 @@ every day in Rust.
|
||||||
|
|
||||||
## Key examples
|
## Key examples
|
||||||
|
|
||||||
Let's go through a couple of important `std` types that leverage interior mutability.
|
Let's go through a couple of important `std` types that leverage interior mutability.\
|
||||||
These are types that you'll encounter somewhat often in Rust code, especially if you peek under the hood of
|
These are types that you'll encounter somewhat often in Rust code, especially if you peek under the hood of
|
||||||
some the libraries you use.
|
some the libraries you use.
|
||||||
|
|
||||||
### Reference counting
|
### Reference counting
|
||||||
|
|
||||||
`Rc` is a reference-counted pointer.
|
`Rc` is a reference-counted pointer.\
|
||||||
It wraps around a value and keeps track of how many references to the value exist.
|
It wraps around a value and keeps track of how many references to the value exist.
|
||||||
When the last reference is dropped, the value is deallocated.
|
When the last reference is dropped, the value is deallocated.\
|
||||||
The value wrapped in an `Rc` is immutable: you can only get shared references to it.
|
The value wrapped in an `Rc` is immutable: you can only get shared references to it.
|
||||||
|
|
||||||
```rust
|
```rust
|
||||||
|
|
|
@ -1,6 +1,6 @@
|
||||||
# Two-way communication
|
# Two-way communication
|
||||||
|
|
||||||
In our current client-server implementation, communication flows in one direction: from the client to the server.
|
In our current client-server implementation, communication flows in one direction: from the client to the server.\
|
||||||
The client has no way of knowing if the server received the message, executed it successfully, or failed.
|
The client has no way of knowing if the server received the message, executed it successfully, or failed.
|
||||||
That's not ideal.
|
That's not ideal.
|
||||||
|
|
||||||
|
@ -8,7 +8,7 @@ To solve this issue, we can introduce a two-way communication system.
|
||||||
|
|
||||||
## Response channel
|
## Response channel
|
||||||
|
|
||||||
We need a way for the server to send a response back to the client.
|
We need a way for the server to send a response back to the client.\
|
||||||
There are various ways to do this, but the simplest option is to include a `Sender` channel in
|
There are various ways to do this, but the simplest option is to include a `Sender` channel in
|
||||||
the message that the client sends to the server. After processing the message, the server can use
|
the message that the client sends to the server. After processing the message, the server can use
|
||||||
this channel to send a response back to the client.
|
this channel to send a response back to the client.
|
||||||
|
|
|
@ -1,18 +1,18 @@
|
||||||
# Bounded vs unbounded channels
|
# Bounded vs unbounded channels
|
||||||
|
|
||||||
So far we've been using unbounded channels.
|
So far we've been using unbounded channels.\
|
||||||
You can send as many messages as you want, and the channel will grow to accommodate them.
|
You can send as many messages as you want, and the channel will grow to accommodate them.\
|
||||||
In a multi-producer single-consumer scenario, this can be problematic: if the producers
|
In a multi-producer single-consumer scenario, this can be problematic: if the producers
|
||||||
enqueues messages at a faster rate than the consumer can process them, the channel will
|
enqueues messages at a faster rate than the consumer can process them, the channel will
|
||||||
keep growing, potentially consuming all available memory.
|
keep growing, potentially consuming all available memory.
|
||||||
|
|
||||||
Our recommendation is to **never** use an unbounded channel in a production system.
|
Our recommendation is to **never** use an unbounded channel in a production system.\
|
||||||
You should always enforce an upper limit on the number of messages that can be enqueued using a
|
You should always enforce an upper limit on the number of messages that can be enqueued using a
|
||||||
**bounded channel**.
|
**bounded channel**.
|
||||||
|
|
||||||
## Bounded channels
|
## Bounded channels
|
||||||
|
|
||||||
A bounded channel has a fixed capacity.
|
A bounded channel has a fixed capacity.\
|
||||||
You can create one by calling `sync_channel` with a capacity greater than zero:
|
You can create one by calling `sync_channel` with a capacity greater than zero:
|
||||||
|
|
||||||
```rust
|
```rust
|
||||||
|
@ -21,23 +21,23 @@ use std::sync::mpsc::sync_channel;
|
||||||
let (sender, receiver) = sync_channel(10);
|
let (sender, receiver) = sync_channel(10);
|
||||||
```
|
```
|
||||||
|
|
||||||
`receiver` has the same type as before, `Receiver<T>`.
|
`receiver` has the same type as before, `Receiver<T>`.\
|
||||||
`sender`, instead, is an instance of `SyncSender<T>`.
|
`sender`, instead, is an instance of `SyncSender<T>`.
|
||||||
|
|
||||||
### Sending messages
|
### Sending messages
|
||||||
|
|
||||||
You have two different methods to send messages through a `SyncSender`:
|
You have two different methods to send messages through a `SyncSender`:
|
||||||
|
|
||||||
- `send`: if there is space in the channel, it will enqueue the message and return `Ok(())`.
|
- `send`: if there is space in the channel, it will enqueue the message and return `Ok(())`.\
|
||||||
If the channel is full, it will block and wait until there is space available.
|
If the channel is full, it will block and wait until there is space available.
|
||||||
- `try_send`: if there is space in the channel, it will enqueue the message and return `Ok(())`.
|
- `try_send`: if there is space in the channel, it will enqueue the message and return `Ok(())`.\
|
||||||
If the channel is full, it will return `Err(TrySendError::Full(value))`, where `value` is the message that couldn't be sent.
|
If the channel is full, it will return `Err(TrySendError::Full(value))`, where `value` is the message that couldn't be sent.
|
||||||
|
|
||||||
Depending on your use case, you might want to use one or the other.
|
Depending on your use case, you might want to use one or the other.
|
||||||
|
|
||||||
### Backpressure
|
### Backpressure
|
||||||
|
|
||||||
The main advantage of using bounded channels is that they provide a form of **backpressure**.
|
The main advantage of using bounded channels is that they provide a form of **backpressure**.\
|
||||||
They force the producers to slow down if the consumer can't keep up.
|
They force the producers to slow down if the consumer can't keep up.
|
||||||
The backpressure can then propagate through the system, potentially affecting the whole architecture and
|
The backpressure can then propagate through the system, potentially affecting the whole architecture and
|
||||||
preventing end users from overwhelming the system with requests.
|
preventing end users from overwhelming the system with requests.
|
|
@ -1,6 +1,6 @@
|
||||||
# Update operations
|
# Update operations
|
||||||
|
|
||||||
So far we've implemented only insertion and retrieval operations.
|
So far we've implemented only insertion and retrieval operations.\
|
||||||
Let's see how we can expand the system to provide an update operation.
|
Let's see how we can expand the system to provide an update operation.
|
||||||
|
|
||||||
## Legacy updates
|
## Legacy updates
|
||||||
|
@ -18,7 +18,7 @@ There are a few ways to work around this limitation. We'll explore a few of them
|
||||||
|
|
||||||
### Patching
|
### Patching
|
||||||
|
|
||||||
We can't send a `&mut Ticket` over a channel, therefore we can't mutate on the client-side.
|
We can't send a `&mut Ticket` over a channel, therefore we can't mutate on the client-side.\
|
||||||
Can we mutate on the server-side?
|
Can we mutate on the server-side?
|
||||||
|
|
||||||
We can, if we tell the server what needs to be changed. In other words, if we send a **patch** to the server:
|
We can, if we tell the server what needs to be changed. In other words, if we send a **patch** to the server:
|
||||||
|
@ -32,7 +32,7 @@ struct TicketPatch {
|
||||||
}
|
}
|
||||||
```
|
```
|
||||||
|
|
||||||
The `id` field is mandatory, since it's required to identify the ticket that needs to be updated.
|
The `id` field is mandatory, since it's required to identify the ticket that needs to be updated.\
|
||||||
All other fields are optional:
|
All other fields are optional:
|
||||||
|
|
||||||
- If a field is `None`, it means that the field should not be changed.
|
- If a field is `None`, it means that the field should not be changed.
|
||||||
|
|
|
@ -1,13 +1,13 @@
|
||||||
# Locks, `Send` and `Arc`
|
# Locks, `Send` and `Arc`
|
||||||
|
|
||||||
The patching strategy you just implemented has a major drawback: it's racy.
|
The patching strategy you just implemented has a major drawback: it's racy.\
|
||||||
If two clients send patches for the same ticket roughly at same time, the server will apply them in an arbitrary order.
|
If two clients send patches for the same ticket roughly at same time, the server will apply them in an arbitrary order.
|
||||||
Whoever enqueues their patch last will overwrite the changes made by the other client.
|
Whoever enqueues their patch last will overwrite the changes made by the other client.
|
||||||
|
|
||||||
## Version numbers
|
## Version numbers
|
||||||
|
|
||||||
We could try to fix this by using a **version number**.
|
We could try to fix this by using a **version number**.\
|
||||||
Each ticket gets assigned a version number upon creation, set to `0`.
|
Each ticket gets assigned a version number upon creation, set to `0`.\
|
||||||
Whenever a client sends a patch, they must include the current version number of the ticket alongside the
|
Whenever a client sends a patch, they must include the current version number of the ticket alongside the
|
||||||
desired changes. The server will only apply the patch if the version number matches the one it has stored.
|
desired changes. The server will only apply the patch if the version number matches the one it has stored.
|
||||||
|
|
||||||
|
@ -15,24 +15,24 @@ In the scenario described above, the server would reject the second patch, becau
|
||||||
have been incremented by the first patch and thus wouldn't match the one sent by the second client.
|
have been incremented by the first patch and thus wouldn't match the one sent by the second client.
|
||||||
|
|
||||||
This approach is fairly common in distributed systems (e.g. when client and servers don't share memory),
|
This approach is fairly common in distributed systems (e.g. when client and servers don't share memory),
|
||||||
and it is known as **optimistic concurrency control**.
|
and it is known as **optimistic concurrency control**.\
|
||||||
The idea is that most of the time, conflicts won't happen, so we can optimize for the common case.
|
The idea is that most of the time, conflicts won't happen, so we can optimize for the common case.
|
||||||
You know enough about Rust by now to implement this strategy on your own as a bonus exercise, if you want to.
|
You know enough about Rust by now to implement this strategy on your own as a bonus exercise, if you want to.
|
||||||
|
|
||||||
## Locking
|
## Locking
|
||||||
|
|
||||||
We can also fix the race condition by introducing a **lock**.
|
We can also fix the race condition by introducing a **lock**.\
|
||||||
Whenever a client wants to update a ticket, they must first acquire a lock on it. While the lock is active,
|
Whenever a client wants to update a ticket, they must first acquire a lock on it. While the lock is active,
|
||||||
no other client can modify the ticket.
|
no other client can modify the ticket.
|
||||||
|
|
||||||
Rust's standard library provides two different locking primitives: `Mutex<T>` and `RwLock<T>`.
|
Rust's standard library provides two different locking primitives: `Mutex<T>` and `RwLock<T>`.\
|
||||||
Let's start with `Mutex<T>`. It stands for **mut**ual **ex**clusion, and it's the simplest kind of lock:
|
Let's start with `Mutex<T>`. It stands for **mut**ual **ex**clusion, and it's the simplest kind of lock:
|
||||||
it allows only one thread to access the data, no matter if it's for reading or writing.
|
it allows only one thread to access the data, no matter if it's for reading or writing.
|
||||||
|
|
||||||
`Mutex<T>` wraps the data it protects, and it's therefore generic over the type of the data.
|
`Mutex<T>` wraps the data it protects, and it's therefore generic over the type of the data.\
|
||||||
You can't access the data directly: the type system forces you to acquire a lock first using either `Mutex::lock` or
|
You can't access the data directly: the type system forces you to acquire a lock first using either `Mutex::lock` or
|
||||||
`Mutex::try_lock`. The former blocks until the lock is acquired, the latter returns immediately with an error if the lock
|
`Mutex::try_lock`. The former blocks until the lock is acquired, the latter returns immediately with an error if the lock
|
||||||
can't be acquired.
|
can't be acquired.\
|
||||||
Both methods return a guard object that dereferences to the data, allowing you to modify it. The lock is released when
|
Both methods return a guard object that dereferences to the data, allowing you to modify it. The lock is released when
|
||||||
the guard is dropped.
|
the guard is dropped.
|
||||||
|
|
||||||
|
@ -57,10 +57,10 @@ drop(guard)
|
||||||
|
|
||||||
## Locking granularity
|
## Locking granularity
|
||||||
|
|
||||||
What should our `Mutex` wrap?
|
What should our `Mutex` wrap?\
|
||||||
The simplest option would be the wrap the entire `TicketStore` in a single `Mutex`.
|
The simplest option would be the wrap the entire `TicketStore` in a single `Mutex`.\
|
||||||
This would work, but it would severely limit the system's performance: you wouldn't be able to read tickets in parallel,
|
This would work, but it would severely limit the system's performance: you wouldn't be able to read tickets in parallel,
|
||||||
because every read would have to wait for the lock to be released.
|
because every read would have to wait for the lock to be released.\
|
||||||
This is known as **coarse-grained locking**.
|
This is known as **coarse-grained locking**.
|
||||||
|
|
||||||
It would be better to use **fine-grained locking**, where each ticket is protected by its own lock.
|
It would be better to use **fine-grained locking**, where each ticket is protected by its own lock.
|
||||||
|
@ -74,15 +74,15 @@ struct TicketStore {
|
||||||
```
|
```
|
||||||
|
|
||||||
This approach is more efficient, but it has a downside: `TicketStore` has to become **aware** of the multithreaded
|
This approach is more efficient, but it has a downside: `TicketStore` has to become **aware** of the multithreaded
|
||||||
nature of the system; up until now, `TicketStore` has been blissfully ignored the existence of threads.
|
nature of the system; up until now, `TicketStore` has been blissfully ignored the existence of threads.\
|
||||||
Let's go for it anyway.
|
Let's go for it anyway.
|
||||||
|
|
||||||
## Who holds the lock?
|
## Who holds the lock?
|
||||||
|
|
||||||
For the whole scheme to work, the lock must be passed to the client that wants to modify the ticket.
|
For the whole scheme to work, the lock must be passed to the client that wants to modify the ticket.\
|
||||||
The client can then directly modify the ticket (as if they had a `&mut Ticket`) and release the lock when they're done.
|
The client can then directly modify the ticket (as if they had a `&mut Ticket`) and release the lock when they're done.
|
||||||
|
|
||||||
This is a bit tricky.
|
This is a bit tricky.\
|
||||||
We can't send a `Mutex<Ticket>` over a channel, because `Mutex` is not `Clone` and
|
We can't send a `Mutex<Ticket>` over a channel, because `Mutex` is not `Clone` and
|
||||||
we can't move it out of the `TicketStore`. Could we send the `MutexGuard` instead?
|
we can't move it out of the `TicketStore`. Could we send the `MutexGuard` instead?
|
||||||
|
|
||||||
|
@ -131,22 +131,22 @@ note: required because it's used within this closure
|
||||||
|
|
||||||
## `Send`
|
## `Send`
|
||||||
|
|
||||||
`Send` is a marker trait that indicates that a type can be safely transferred from one thread to another.
|
`Send` is a marker trait that indicates that a type can be safely transferred from one thread to another.\
|
||||||
`Send` is also an auto-trait, just like `Sized`; it's automatically implemented (or not implemented) for your type
|
`Send` is also an auto-trait, just like `Sized`; it's automatically implemented (or not implemented) for your type
|
||||||
by the compiler, based on its definition.
|
by the compiler, based on its definition.\
|
||||||
You can also implement `Send` manually for your types, but it requires `unsafe` since you have to guarantee that the
|
You can also implement `Send` manually for your types, but it requires `unsafe` since you have to guarantee that the
|
||||||
type is indeed safe to send between threads for reasons that the compiler can't automatically verify.
|
type is indeed safe to send between threads for reasons that the compiler can't automatically verify.
|
||||||
|
|
||||||
### Channel requirements
|
### Channel requirements
|
||||||
|
|
||||||
`Sender<T>`, `SyncSender<T>` and `Receiver<T>` are `Send` if and only if `T` is `Send`.
|
`Sender<T>`, `SyncSender<T>` and `Receiver<T>` are `Send` if and only if `T` is `Send`.\
|
||||||
That's because they are used to send values between threads, and if the value itself is not `Send`, it would be
|
That's because they are used to send values between threads, and if the value itself is not `Send`, it would be
|
||||||
unsafe to send it between threads.
|
unsafe to send it between threads.
|
||||||
|
|
||||||
### `MutexGuard`
|
### `MutexGuard`
|
||||||
|
|
||||||
`MutexGuard` is not `Send` because the underlying operating system primitives that `Mutex` uses to implement
|
`MutexGuard` is not `Send` because the underlying operating system primitives that `Mutex` uses to implement
|
||||||
the lock require (on some platforms) that the lock must be released by the same thread that acquired it.
|
the lock require (on some platforms) that the lock must be released by the same thread that acquired it.\
|
||||||
If we were to send a `MutexGuard` to another thread, the lock would be released by a different thread, which would
|
If we were to send a `MutexGuard` to another thread, the lock would be released by a different thread, which would
|
||||||
lead to undefined behavior.
|
lead to undefined behavior.
|
||||||
|
|
||||||
|
@ -160,7 +160,7 @@ Summing it up:
|
||||||
case for `Ticket`.
|
case for `Ticket`.
|
||||||
At the same time, we can't move the `Mutex` out of the `TicketStore` nor clone it.
|
At the same time, we can't move the `Mutex` out of the `TicketStore` nor clone it.
|
||||||
|
|
||||||
How can we solve this conundrum?
|
How can we solve this conundrum?\
|
||||||
We need to look at the problem from a different angle.
|
We need to look at the problem from a different angle.
|
||||||
To lock a `Mutex`, we don't need an owned value. A shared reference is enough, since `Mutex` uses internal mutability:
|
To lock a `Mutex`, we don't need an owned value. A shared reference is enough, since `Mutex` uses internal mutability:
|
||||||
|
|
||||||
|
@ -173,15 +173,15 @@ impl<T> Mutex<T> {
|
||||||
}
|
}
|
||||||
```
|
```
|
||||||
|
|
||||||
It is therefore enough to send a shared reference to the client.
|
It is therefore enough to send a shared reference to the client.\
|
||||||
We can't do that directly, though, because the reference would have to be `'static` and that's not the case.
|
We can't do that directly, though, because the reference would have to be `'static` and that's not the case.\
|
||||||
In a way, we need an "owned shared reference". It turns out that Rust has a type that fits the bill: `Arc`.
|
In a way, we need an "owned shared reference". It turns out that Rust has a type that fits the bill: `Arc`.
|
||||||
|
|
||||||
## `Arc` to the rescue
|
## `Arc` to the rescue
|
||||||
|
|
||||||
`Arc` stands for **atomic reference counting**.
|
`Arc` stands for **atomic reference counting**.\
|
||||||
`Arc` wraps around a value and keeps track of how many references to the value exist.
|
`Arc` wraps around a value and keeps track of how many references to the value exist.
|
||||||
When the last reference is dropped, the value is deallocated.
|
When the last reference is dropped, the value is deallocated.\
|
||||||
The value wrapped in an `Arc` is immutable: you can only get shared references to it.
|
The value wrapped in an `Arc` is immutable: you can only get shared references to it.
|
||||||
|
|
||||||
```rust
|
```rust
|
||||||
|
|
|
@ -3,11 +3,11 @@
|
||||||
Our new `TicketStore` works, but its read performance is not great: there can only be one client at a time
|
Our new `TicketStore` works, but its read performance is not great: there can only be one client at a time
|
||||||
reading a specific ticket, because `Mutex<T>` doesn't distinguish between readers and writers.
|
reading a specific ticket, because `Mutex<T>` doesn't distinguish between readers and writers.
|
||||||
|
|
||||||
We can solve the issue by using a different locking primitive: `RwLock<T>`.
|
We can solve the issue by using a different locking primitive: `RwLock<T>`.\
|
||||||
`RwLock<T>` stands for **read-write lock**. It allows **multiple readers** to access the data simultaneously,
|
`RwLock<T>` stands for **read-write lock**. It allows **multiple readers** to access the data simultaneously,
|
||||||
but only one writer at a time.
|
but only one writer at a time.
|
||||||
|
|
||||||
`RwLock<T>` has two methods to acquire a lock: `read` and `write`.
|
`RwLock<T>` has two methods to acquire a lock: `read` and `write`.\
|
||||||
`read` returns a guard that allows you to read the data, while `write` returns a guard that allows you to modify it.
|
`read` returns a guard that allows you to read the data, while `write` returns a guard that allows you to modify it.
|
||||||
|
|
||||||
```rust
|
```rust
|
||||||
|
@ -31,13 +31,13 @@ Why would you ever use `Mutex<T>` if you can use `RwLock<T>` instead?
|
||||||
|
|
||||||
There are two key reasons:
|
There are two key reasons:
|
||||||
|
|
||||||
- Locking a `RwLock<T>` is more expensive than locking a `Mutex<T>`.
|
- Locking a `RwLock<T>` is more expensive than locking a `Mutex<T>`.\
|
||||||
This is because `RwLock<T>` has to keep track of the number of active readers and writers, while `Mutex<T>`
|
This is because `RwLock<T>` has to keep track of the number of active readers and writers, while `Mutex<T>`
|
||||||
only has to keep track of whether the lock is held or not.
|
only has to keep track of whether the lock is held or not.
|
||||||
This performance overhead is not an issue if there are more readers than writers, but if the workload
|
This performance overhead is not an issue if there are more readers than writers, but if the workload
|
||||||
is write-heavy `Mutex<T>` might be a better choice.
|
is write-heavy `Mutex<T>` might be a better choice.
|
||||||
- `RwLock<T>` can cause **writer starvation**.
|
- `RwLock<T>` can cause **writer starvation**.\
|
||||||
If there are always readers waiting to acquire the lock, writers might never get a chance to run.
|
If there are always readers waiting to acquire the lock, writers might never get a chance to run.\
|
||||||
`RwLock<T>` doesn't provide any guarantees about the order in which readers and writers are granted access to the lock.
|
`RwLock<T>` doesn't provide any guarantees about the order in which readers and writers are granted access to the lock.
|
||||||
It depends on the policy implemented by the underlying OS, which might not be fair to writers.
|
It depends on the policy implemented by the underlying OS, which might not be fair to writers.
|
||||||
|
|
||||||
|
|
|
@ -10,7 +10,7 @@ Our first implementation of a multithreaded ticket store used:
|
||||||
- multiple clients sending requests to it via channels from their own threads.
|
- multiple clients sending requests to it via channels from their own threads.
|
||||||
|
|
||||||
No locking of the state was necessary, since the server was the only one modifying the state. That's because
|
No locking of the state was necessary, since the server was the only one modifying the state. That's because
|
||||||
the "inbox" channel naturally **serialized** incoming requests: the server would process them one by one.
|
the "inbox" channel naturally **serialized** incoming requests: the server would process them one by one.\
|
||||||
We've already discussed the limitations of this approach when it comes to patching behaviour, but we didn't
|
We've already discussed the limitations of this approach when it comes to patching behaviour, but we didn't
|
||||||
discuss the performance implications of the original design: the server could only process one request at a time,
|
discuss the performance implications of the original design: the server could only process one request at a time,
|
||||||
including reads.
|
including reads.
|
||||||
|
@ -37,17 +37,17 @@ We have two problems to solve:
|
||||||
### Sharing `TicketStore` across threads
|
### Sharing `TicketStore` across threads
|
||||||
|
|
||||||
We want all threads to refer to the same state, otherwise we don't really have a multithreaded system—we're just
|
We want all threads to refer to the same state, otherwise we don't really have a multithreaded system—we're just
|
||||||
running multiple single-threaded systems in parallel.
|
running multiple single-threaded systems in parallel.\
|
||||||
We've already encountered this problem when we tried to share a lock across threads: we can use an `Arc`.
|
We've already encountered this problem when we tried to share a lock across threads: we can use an `Arc`.
|
||||||
|
|
||||||
### Synchronizing access to the store
|
### Synchronizing access to the store
|
||||||
|
|
||||||
There is one interaction that's still lockless thanks to the serialization provided by the channels: inserting
|
There is one interaction that's still lockless thanks to the serialization provided by the channels: inserting
|
||||||
(or removing) a ticket from the store.
|
(or removing) a ticket from the store.\
|
||||||
If we remove the channels, we need to introduce (another) lock to synchronize access to the `TicketStore` itself.
|
If we remove the channels, we need to introduce (another) lock to synchronize access to the `TicketStore` itself.
|
||||||
|
|
||||||
If we use a `Mutex`, then it makes no sense to use an additional `RwLock` for each ticket: the `Mutex` will
|
If we use a `Mutex`, then it makes no sense to use an additional `RwLock` for each ticket: the `Mutex` will
|
||||||
already serialize access to the entire store, so we wouldn't be able to read tickets in parallel anyway.
|
already serialize access to the entire store, so we wouldn't be able to read tickets in parallel anyway.\
|
||||||
If we use a `RwLock`, instead, we can read tickets in parallel. We just to pause all reads while inserting
|
If we use a `RwLock`, instead, we can read tickets in parallel. We just to pause all reads while inserting
|
||||||
or removing a ticket.
|
or removing a ticket.
|
||||||
|
|
||||||
|
|
|
@ -2,27 +2,27 @@
|
||||||
|
|
||||||
Before we wrap up this chapter, let's talk about another key trait in Rust's standard library: `Sync`.
|
Before we wrap up this chapter, let's talk about another key trait in Rust's standard library: `Sync`.
|
||||||
|
|
||||||
`Sync` is an auto trait, just like `Send`.
|
`Sync` is an auto trait, just like `Send`.\
|
||||||
It is automatically implemented by all types that can be safely **shared** between threads.
|
It is automatically implemented by all types that can be safely **shared** between threads.
|
||||||
|
|
||||||
In order words: `T: Sync` means that `&T` is `Send`.
|
In order words: `T: Sync` means that `&T` is `Send`.
|
||||||
|
|
||||||
## `Sync` doesn't imply `Send`
|
## `Sync` doesn't imply `Send`
|
||||||
|
|
||||||
It's important to note that `Sync` doesn't imply `Send`.
|
It's important to note that `Sync` doesn't imply `Send`.\
|
||||||
For example: `MutexGuard` is not `Send`, but it is `Sync`.
|
For example: `MutexGuard` is not `Send`, but it is `Sync`.
|
||||||
|
|
||||||
It isn't `Send` because the lock must be released on the same thread that acquired it, therefore we don't
|
It isn't `Send` because the lock must be released on the same thread that acquired it, therefore we don't
|
||||||
want `MutexGuard` to be dropped on a different thread.
|
want `MutexGuard` to be dropped on a different thread.\
|
||||||
But it is `Sync`, because giving a `&MutexGuard` to another thread has no impact on where the lock is released.
|
But it is `Sync`, because giving a `&MutexGuard` to another thread has no impact on where the lock is released.
|
||||||
|
|
||||||
## `Send` doesn't imply `Sync`
|
## `Send` doesn't imply `Sync`
|
||||||
|
|
||||||
The opposite is also true: `Send` doesn't imply `Sync`.
|
The opposite is also true: `Send` doesn't imply `Sync`.\
|
||||||
For example: `RefCell<T>` is `Send` (if `T` is `Send`), but it is not `Sync`.
|
For example: `RefCell<T>` is `Send` (if `T` is `Send`), but it is not `Sync`.
|
||||||
|
|
||||||
`RefCell<T>` performs runtime borrow checking, but the counters it uses to track borrows are not thread-safe.
|
`RefCell<T>` performs runtime borrow checking, but the counters it uses to track borrows are not thread-safe.
|
||||||
Therefore, having multiple threads holding a `&RefCell` would lead to a data race, with potentially
|
Therefore, having multiple threads holding a `&RefCell` would lead to a data race, with potentially
|
||||||
multiple threads obtaining mutable references to the same data. Hence `RefCell` is not `Sync`.
|
multiple threads obtaining mutable references to the same data. Hence `RefCell` is not `Sync`.\
|
||||||
`Send` is fine, instead, because when we send a `RefCell` to another thread we're not
|
`Send` is fine, instead, because when we send a `RefCell` to another thread we're not
|
||||||
leaving behind any references to the data it contains, hence no risk of concurrent mutable access.
|
leaving behind any references to the data it contains, hence no risk of concurrent mutable access.
|
|
@ -1,6 +1,6 @@
|
||||||
# Async Rust
|
# Async Rust
|
||||||
|
|
||||||
Threads are not the only way to write concurrent programs in Rust.
|
Threads are not the only way to write concurrent programs in Rust.\
|
||||||
In this chapter we'll explore another approach: **asynchronous programming**.
|
In this chapter we'll explore another approach: **asynchronous programming**.
|
||||||
|
|
||||||
In particular, you'll get an introduction to:
|
In particular, you'll get an introduction to:
|
||||||
|
|
|
@ -1,16 +1,16 @@
|
||||||
# Asynchronous functions
|
# Asynchronous functions
|
||||||
|
|
||||||
All the functions and methods you've written so far were eager.
|
All the functions and methods you've written so far were eager.\
|
||||||
Nothing happened until you invoked them. But once you did, they ran to
|
Nothing happened until you invoked them. But once you did, they ran to
|
||||||
completion: they did **all** their work, and then returned their output.
|
completion: they did **all** their work, and then returned their output.
|
||||||
|
|
||||||
Sometimes that's undesirable.
|
Sometimes that's undesirable.\
|
||||||
For example, if you're writing an HTTP server, there might be a lot of
|
For example, if you're writing an HTTP server, there might be a lot of
|
||||||
**waiting**: waiting for the request body to arrive, waiting for the
|
**waiting**: waiting for the request body to arrive, waiting for the
|
||||||
database to respond, waiting for a downstream service to reply, etc.
|
database to respond, waiting for a downstream service to reply, etc.
|
||||||
|
|
||||||
What if you could do something else while you're waiting?
|
What if you could do something else while you're waiting?\
|
||||||
What if you could choose to give up midway through a computation?
|
What if you could choose to give up midway through a computation?\
|
||||||
What if you could choose to prioritise another task over the current one?
|
What if you could choose to prioritise another task over the current one?
|
||||||
|
|
||||||
That's where **asynchronous functions** come in.
|
That's where **asynchronous functions** come in.
|
||||||
|
@ -38,7 +38,7 @@ fn run() {
|
||||||
}
|
}
|
||||||
```
|
```
|
||||||
|
|
||||||
Nothing happens!
|
Nothing happens!\
|
||||||
Rust doesn't start executing `bind_random` when you call it,
|
Rust doesn't start executing `bind_random` when you call it,
|
||||||
not even as a background task (as you might expect based on your experience
|
not even as a background task (as you might expect based on your experience
|
||||||
with other languages).
|
with other languages).
|
||||||
|
@ -73,13 +73,13 @@ has run to completion—e.g. until the `TcpListener` has been created in the exa
|
||||||
|
|
||||||
## Runtimes
|
## Runtimes
|
||||||
|
|
||||||
If you're puzzled, you're right to be!
|
If you're puzzled, you're right to be!\
|
||||||
We've just said that the perk of asynchronous functions
|
We've just said that the perk of asynchronous functions
|
||||||
is that they don't do **all** their work at once. We then introduced `.await`, which
|
is that they don't do **all** their work at once. We then introduced `.await`, which
|
||||||
doesn't return until the asynchronous function has run to completion. Haven't we
|
doesn't return until the asynchronous function has run to completion. Haven't we
|
||||||
just re-introduced the problem we were trying to solve? What's the point?
|
just re-introduced the problem we were trying to solve? What's the point?
|
||||||
|
|
||||||
Not quite! A lot happens behind the scenes when you call `.await`!
|
Not quite! A lot happens behind the scenes when you call `.await`!\
|
||||||
You're yielding control to an **async runtime**, also known as an **async executor**.
|
You're yielding control to an **async runtime**, also known as an **async executor**.
|
||||||
Executors are where the magic happens: they are in charge of managing all your
|
Executors are where the magic happens: they are in charge of managing all your
|
||||||
ongoing asynchronous **tasks**. In particular, they balance two different goals:
|
ongoing asynchronous **tasks**. In particular, they balance two different goals:
|
||||||
|
@ -130,10 +130,10 @@ fn main() {
|
||||||
|
|
||||||
### `#[tokio::test]`
|
### `#[tokio::test]`
|
||||||
|
|
||||||
The same goes for tests: they must be synchronous functions.
|
The same goes for tests: they must be synchronous functions.\
|
||||||
Each test function is run in its own thread, and you're responsible for
|
Each test function is run in its own thread, and you're responsible for
|
||||||
setting up and launching an async runtime if you need to run async code
|
setting up and launching an async runtime if you need to run async code
|
||||||
in your tests.
|
in your tests.\
|
||||||
`tokio` provides a `#[tokio::test]` macro to make this easier:
|
`tokio` provides a `#[tokio::test]` macro to make this easier:
|
||||||
|
|
||||||
```rust
|
```rust
|
||||||
|
|
|
@ -12,12 +12,12 @@ pub async fn echo(listener: TcpListener) -> Result<(), anyhow::Error> {
|
||||||
}
|
}
|
||||||
```
|
```
|
||||||
|
|
||||||
This is not bad!
|
This is not bad!\
|
||||||
If a long time passes between two incoming connections, the `echo` function will be idle
|
If a long time passes between two incoming connections, the `echo` function will be idle
|
||||||
(since `TcpListener::accept` is an asynchronous function), thus allowing the executor
|
(since `TcpListener::accept` is an asynchronous function), thus allowing the executor
|
||||||
to run other tasks in the meantime.
|
to run other tasks in the meantime.
|
||||||
|
|
||||||
But how can we actually have multiple tasks running concurrently?
|
But how can we actually have multiple tasks running concurrently?\
|
||||||
If we always run our asynchronous functions until completion (by using `.await`), we'll never
|
If we always run our asynchronous functions until completion (by using `.await`), we'll never
|
||||||
have more than one task running at a time.
|
have more than one task running at a time.
|
||||||
|
|
||||||
|
@ -25,7 +25,7 @@ This is where the `tokio::spawn` function comes in.
|
||||||
|
|
||||||
## `tokio::spawn`
|
## `tokio::spawn`
|
||||||
|
|
||||||
`tokio::spawn` allows you to hand off a task to the executor, **without waiting for it to complete**.
|
`tokio::spawn` allows you to hand off a task to the executor, **without waiting for it to complete**.\
|
||||||
Whenever you invoke `tokio::spawn`, you're telling `tokio` to continue running
|
Whenever you invoke `tokio::spawn`, you're telling `tokio` to continue running
|
||||||
the spawned task, in the background, **concurrently** with the task that spawned it.
|
the spawned task, in the background, **concurrently** with the task that spawned it.
|
||||||
|
|
||||||
|
@ -56,7 +56,7 @@ to define a separate async function.
|
||||||
|
|
||||||
### `JoinHandle`
|
### `JoinHandle`
|
||||||
|
|
||||||
`tokio::spawn` returns a `JoinHandle`.
|
`tokio::spawn` returns a `JoinHandle`.\
|
||||||
You can use `JoinHandle` to `.await` the background task, in the same way
|
You can use `JoinHandle` to `.await` the background task, in the same way
|
||||||
we used `join` for spawned threads.
|
we used `join` for spawned threads.
|
||||||
|
|
||||||
|
@ -83,7 +83,7 @@ pub async fn do_work() {
|
||||||
|
|
||||||
### Panic boundary
|
### Panic boundary
|
||||||
|
|
||||||
If a task spawned with `tokio::spawn` panics, the panic will be caught by the executor.
|
If a task spawned with `tokio::spawn` panics, the panic will be caught by the executor.\
|
||||||
If you don't `.await` the corresponding `JoinHandle`, the panic won't be propagated to the spawner.
|
If you don't `.await` the corresponding `JoinHandle`, the panic won't be propagated to the spawner.
|
||||||
Even if you do `.await` the `JoinHandle`, the panic won't be propagated automatically.
|
Even if you do `.await` the `JoinHandle`, the panic won't be propagated automatically.
|
||||||
Awaiting a `JoinHandle` returns a `Result`, with [`JoinError`](https://docs.rs/tokio/latest/tokio/task/struct.JoinError.html)
|
Awaiting a `JoinHandle` returns a `Result`, with [`JoinError`](https://docs.rs/tokio/latest/tokio/task/struct.JoinError.html)
|
||||||
|
|
|
@ -19,7 +19,7 @@ You can configure your runtime via `tokio::runtime::Builder`:
|
||||||
### Current thread runtime
|
### Current thread runtime
|
||||||
|
|
||||||
The current-thread runtime, as the name implies, relies exclusively on the OS thread
|
The current-thread runtime, as the name implies, relies exclusively on the OS thread
|
||||||
it was launched on to schedule and execute tasks.
|
it was launched on to schedule and execute tasks.\
|
||||||
When using the current-thread runtime, you have **concurrency** but no **parallelism**:
|
When using the current-thread runtime, you have **concurrency** but no **parallelism**:
|
||||||
asynchronous tasks will be interleaved, but there will always be at most one task running
|
asynchronous tasks will be interleaved, but there will always be at most one task running
|
||||||
at any given time.
|
at any given time.
|
||||||
|
@ -30,10 +30,10 @@ When using the multithreaded runtime, instead, there can up to `N` tasks running
|
||||||
_in parallel_ at any given time, where `N` is the number of threads used by the
|
_in parallel_ at any given time, where `N` is the number of threads used by the
|
||||||
runtime. By default, `N` matches the number of available CPU cores.
|
runtime. By default, `N` matches the number of available CPU cores.
|
||||||
|
|
||||||
There's more: `tokio` performs **work-stealing**.
|
There's more: `tokio` performs **work-stealing**.\
|
||||||
If a thread is idle, it won't wait around: it'll try to find a new task that's ready for
|
If a thread is idle, it won't wait around: it'll try to find a new task that's ready for
|
||||||
execution, either from a global queue or by stealing it from the local queue of another
|
execution, either from a global queue or by stealing it from the local queue of another
|
||||||
thread.
|
thread.\
|
||||||
Work-stealing can have significant performance benefits, especially on tail latencies,
|
Work-stealing can have significant performance benefits, especially on tail latencies,
|
||||||
whenever your application is dealing with workloads that are not perfectly balanced
|
whenever your application is dealing with workloads that are not perfectly balanced
|
||||||
across threads.
|
across threads.
|
||||||
|
@ -52,7 +52,7 @@ where
|
||||||
{ /* */ }
|
{ /* */ }
|
||||||
```
|
```
|
||||||
|
|
||||||
Let's ignore the `Future` trait for now to focus on the rest.
|
Let's ignore the `Future` trait for now to focus on the rest.\
|
||||||
`spawn` is asking all its inputs to be `Send` and have a `'static` lifetime.
|
`spawn` is asking all its inputs to be `Send` and have a `'static` lifetime.
|
||||||
|
|
||||||
The `'static` constraint follows the same rationale of the `'static` constraint
|
The `'static` constraint follows the same rationale of the `'static` constraint
|
||||||
|
|
|
@ -12,11 +12,11 @@ pub fn spawn<F>(future: F) -> JoinHandle<F::Output>
|
||||||
{ /* */ }
|
{ /* */ }
|
||||||
```
|
```
|
||||||
|
|
||||||
What does it _actually_ mean for `F` to be `Send`?
|
What does it _actually_ mean for `F` to be `Send`?\
|
||||||
It implies, as we saw in the previous section, that whatever value it captures from the
|
It implies, as we saw in the previous section, that whatever value it captures from the
|
||||||
spawning environment has to be `Send`. But it goes further than that.
|
spawning environment has to be `Send`. But it goes further than that.
|
||||||
|
|
||||||
Any value that's _held across a .await point_ has to be `Send`.
|
Any value that's _held across a .await point_ has to be `Send`.\
|
||||||
Let's look at an example:
|
Let's look at an example:
|
||||||
|
|
||||||
```rust
|
```rust
|
||||||
|
@ -90,8 +90,8 @@ trait Future {
|
||||||
|
|
||||||
### `poll`
|
### `poll`
|
||||||
|
|
||||||
The `poll` method is the heart of the `Future` trait.
|
The `poll` method is the heart of the `Future` trait.\
|
||||||
A future on its own doesn't do anything. It needs to be **polled** to make progress.
|
A future on its own doesn't do anything. It needs to be **polled** to make progress.\
|
||||||
When you call `poll`, you're asking the future to do some work.
|
When you call `poll`, you're asking the future to do some work.
|
||||||
`poll` tries to make progress, and then returns one of the following:
|
`poll` tries to make progress, and then returns one of the following:
|
||||||
|
|
||||||
|
@ -104,13 +104,13 @@ completed, there's nothing left to do.
|
||||||
|
|
||||||
### The role of the runtime
|
### The role of the runtime
|
||||||
|
|
||||||
You'll rarely, if ever, be calling poll directly.
|
You'll rarely, if ever, be calling poll directly.\
|
||||||
That's the job of your async runtime: it has all the required information (the `Context`
|
That's the job of your async runtime: it has all the required information (the `Context`
|
||||||
in `poll`'s signature) to ensure that your futures are making progress whenever they can.
|
in `poll`'s signature) to ensure that your futures are making progress whenever they can.
|
||||||
|
|
||||||
## `async fn` and futures
|
## `async fn` and futures
|
||||||
|
|
||||||
We've worked with the high-level interface, asynchronous functions.
|
We've worked with the high-level interface, asynchronous functions.\
|
||||||
We've now looked at the low-level primitive, the `Future trait`.
|
We've now looked at the low-level primitive, the `Future trait`.
|
||||||
|
|
||||||
How are they related?
|
How are they related?
|
||||||
|
@ -143,10 +143,10 @@ pub enum ExampleFuture {
|
||||||
```
|
```
|
||||||
|
|
||||||
When `example` is called, it returns `ExampleFuture::NotStarted`. The future has never
|
When `example` is called, it returns `ExampleFuture::NotStarted`. The future has never
|
||||||
been polled yet, so nothing has happened.
|
been polled yet, so nothing has happened.\
|
||||||
When the runtime polls it the first time, `ExampleFuture` will advance until the next
|
When the runtime polls it the first time, `ExampleFuture` will advance until the next
|
||||||
`.await` point: it'll stop at the `ExampleFuture::YieldNow(Rc<i32>)` stage of the state
|
`.await` point: it'll stop at the `ExampleFuture::YieldNow(Rc<i32>)` stage of the state
|
||||||
machine, returning `Poll::Pending`.
|
machine, returning `Poll::Pending`.\
|
||||||
When it's polled again, it'll execute the remaining code (`println!`) and
|
When it's polled again, it'll execute the remaining code (`println!`) and
|
||||||
return `Poll::Ready(())`.
|
return `Poll::Ready(())`.
|
||||||
|
|
||||||
|
@ -157,7 +157,7 @@ it cannot be `Send`.
|
||||||
## Yield points
|
## Yield points
|
||||||
|
|
||||||
As you've just seen with `example`, every `.await` point creates a new intermediate
|
As you've just seen with `example`, every `.await` point creates a new intermediate
|
||||||
state in the lifecycle of a future.
|
state in the lifecycle of a future.\
|
||||||
That's why `.await` points are also known as **yield points**: your future _yields control_
|
That's why `.await` points are also known as **yield points**: your future _yields control_
|
||||||
back to the runtime that was polling it, allowing the runtime to pause it and (if necessary)
|
back to the runtime that was polling it, allowing the runtime to pause it and (if necessary)
|
||||||
schedule another task for execution, thus making progress on multiple fronts concurrently.
|
schedule another task for execution, thus making progress on multiple fronts concurrently.
|
||||||
|
|
|
@ -1,6 +1,6 @@
|
||||||
# Don't block the runtime
|
# Don't block the runtime
|
||||||
|
|
||||||
Let's circle back to yield points.
|
Let's circle back to yield points.\
|
||||||
Unlike threads, **Rust tasks cannot be preempted**.
|
Unlike threads, **Rust tasks cannot be preempted**.
|
||||||
|
|
||||||
`tokio` cannot, on its own, decide to pause a task and run another one in its place.
|
`tokio` cannot, on its own, decide to pause a task and run another one in its place.
|
||||||
|
@ -46,7 +46,7 @@ of entries.
|
||||||
## How to avoid blocking
|
## How to avoid blocking
|
||||||
|
|
||||||
OK, so how do you avoid blocking the runtime assuming you _must_ perform an operation
|
OK, so how do you avoid blocking the runtime assuming you _must_ perform an operation
|
||||||
that qualifies or risks qualifying as blocking?
|
that qualifies or risks qualifying as blocking?\
|
||||||
You need to move the work to a different thread. You don't want to use the so-called
|
You need to move the work to a different thread. You don't want to use the so-called
|
||||||
runtime threads, the ones used by `tokio` to run tasks.
|
runtime threads, the ones used by `tokio` to run tasks.
|
||||||
|
|
||||||
|
|
|
@ -73,7 +73,7 @@ async fn run(m: Arc<Mutex<Vec<u64>>>) {
|
||||||
```
|
```
|
||||||
|
|
||||||
Acquiring the lock is now an asynchronous operation, which yields back to the runtime
|
Acquiring the lock is now an asynchronous operation, which yields back to the runtime
|
||||||
if it can't make progress.
|
if it can't make progress.\
|
||||||
Going back to the previous scenario, the following would happen:
|
Going back to the previous scenario, the following would happen:
|
||||||
|
|
||||||
```text
|
```text
|
||||||
|
@ -107,14 +107,14 @@ All good!
|
||||||
|
|
||||||
We've used a single-threaded runtime as the execution context in our
|
We've used a single-threaded runtime as the execution context in our
|
||||||
previous example, but the same risk persists even when using a multithreaded
|
previous example, but the same risk persists even when using a multithreaded
|
||||||
runtime.
|
runtime.\
|
||||||
The only difference is in the number of concurrent tasks required to create the deadlock:
|
The only difference is in the number of concurrent tasks required to create the deadlock:
|
||||||
in a single-threaded runtime, 2 are enough; in a multithreaded runtime, we
|
in a single-threaded runtime, 2 are enough; in a multithreaded runtime, we
|
||||||
would need `N+1` tasks, where `N` is the number of runtime threads.
|
would need `N+1` tasks, where `N` is the number of runtime threads.
|
||||||
|
|
||||||
### Downsides
|
### Downsides
|
||||||
|
|
||||||
Having an async-aware `Mutex` comes with a performance penalty.
|
Having an async-aware `Mutex` comes with a performance penalty.\
|
||||||
If you're confident that the lock isn't under significant contention
|
If you're confident that the lock isn't under significant contention
|
||||||
_and_ you're careful to never hold it across a yield point, you can
|
_and_ you're careful to never hold it across a yield point, you can
|
||||||
still use `std::sync::Mutex` in an asynchronous context.
|
still use `std::sync::Mutex` in an asynchronous context.
|
||||||
|
@ -124,6 +124,6 @@ will incur.
|
||||||
|
|
||||||
## Other primitives
|
## Other primitives
|
||||||
|
|
||||||
We used `Mutex` as an example, but the same applies to `RwLock`, semaphores, etc.
|
We used `Mutex` as an example, but the same applies to `RwLock`, semaphores, etc.\
|
||||||
Prefer async-aware versions when working in an asynchronous context to minimise
|
Prefer async-aware versions when working in an asynchronous context to minimise
|
||||||
the risk of issues.
|
the risk of issues.
|
|
@ -1,6 +1,6 @@
|
||||||
# Cancellation
|
# Cancellation
|
||||||
|
|
||||||
What happens when a pending future is dropped?
|
What happens when a pending future is dropped?\
|
||||||
The runtime will no longer poll it, therefore it won't make any further progress.
|
The runtime will no longer poll it, therefore it won't make any further progress.
|
||||||
In other words, its execution has been **cancelled**.
|
In other words, its execution has been **cancelled**.
|
||||||
|
|
||||||
|
@ -38,7 +38,7 @@ async fn http_call() {
|
||||||
}
|
}
|
||||||
```
|
```
|
||||||
|
|
||||||
Each yield point becomes a **cancellation point**.
|
Each yield point becomes a **cancellation point**.\
|
||||||
`http_call` can't be preempted by the runtime, so it can only be discarded after
|
`http_call` can't be preempted by the runtime, so it can only be discarded after
|
||||||
it has yielded control back to the executor via `.await`.
|
it has yielded control back to the executor via `.await`.
|
||||||
This applies recursively—e.g. `stream.write_all(&request)` is likely to have multiple
|
This applies recursively—e.g. `stream.write_all(&request)` is likely to have multiple
|
||||||
|
@ -49,7 +49,7 @@ finishing transmitting the body.
|
||||||
## Clean up
|
## Clean up
|
||||||
|
|
||||||
Rust's cancellation mechanism is quite powerful—it allows the caller to cancel an ongoing task
|
Rust's cancellation mechanism is quite powerful—it allows the caller to cancel an ongoing task
|
||||||
without needing any form of cooperation from the task itself.
|
without needing any form of cooperation from the task itself.\
|
||||||
At the same time, this can be quite dangerous. It may be desirable to perform a
|
At the same time, this can be quite dangerous. It may be desirable to perform a
|
||||||
**graceful cancellation**, to ensure that some clean-up tasks are performed
|
**graceful cancellation**, to ensure that some clean-up tasks are performed
|
||||||
before aborting the operation.
|
before aborting the operation.
|
||||||
|
@ -87,7 +87,7 @@ The optimal choice is contextual.
|
||||||
## Cancelling spawned tasks
|
## Cancelling spawned tasks
|
||||||
|
|
||||||
When you spawn a task using `tokio::spawn`, you can no longer drop it;
|
When you spawn a task using `tokio::spawn`, you can no longer drop it;
|
||||||
it belongs to the runtime.
|
it belongs to the runtime.\
|
||||||
Nonetheless, you can use its `JoinHandle` to cancel it if needed:
|
Nonetheless, you can use its `JoinHandle` to cancel it if needed:
|
||||||
|
|
||||||
```rust
|
```rust
|
||||||
|
@ -102,7 +102,7 @@ async fn run() {
|
||||||
|
|
||||||
- Be extremely careful when using `tokio`'s `select!` macro to "race" two different futures.
|
- Be extremely careful when using `tokio`'s `select!` macro to "race" two different futures.
|
||||||
Retrying the same task in a loop is dangerous unless you can ensure **cancellation safety**.
|
Retrying the same task in a loop is dangerous unless you can ensure **cancellation safety**.
|
||||||
Check out [`select!`'s documentation](https://tokio.rs/tokio/tutorial/select) for more details.
|
Check out [`select!`'s documentation](https://tokio.rs/tokio/tutorial/select) for more details.\
|
||||||
If you need to interleave two asynchronous streams of data (e.g. a socket and a channel), prefer using
|
If you need to interleave two asynchronous streams of data (e.g. a socket and a channel), prefer using
|
||||||
[`StreamExt::merge`](https://docs.rs/tokio-stream/latest/tokio_stream/trait.StreamExt.html#method.merge) instead.
|
[`StreamExt::merge`](https://docs.rs/tokio-stream/latest/tokio_stream/trait.StreamExt.html#method.merge) instead.
|
||||||
- Rather than "abrupt" cancellation, it can be preferable to rely
|
- Rather than "abrupt" cancellation, it can be preferable to rely
|
||||||
|
|
|
@ -10,25 +10,25 @@ rough edges in your day-to-day work due to some of these missing pieces.
|
||||||
|
|
||||||
A few recommendations for a mostly-pain-free async experience:
|
A few recommendations for a mostly-pain-free async experience:
|
||||||
|
|
||||||
- **Pick a runtime and stick to it.**
|
- **Pick a runtime and stick to it.**\
|
||||||
Some primitives (e.g. timers, I/O) are not portable across runtimes. Trying to
|
Some primitives (e.g. timers, I/O) are not portable across runtimes. Trying to
|
||||||
mix runtimes is likely to cause you pain. Trying to write code that's runtime
|
mix runtimes is likely to cause you pain. Trying to write code that's runtime
|
||||||
agnostic can significantly increase the complexity of your codebase. Avoid it
|
agnostic can significantly increase the complexity of your codebase. Avoid it
|
||||||
if you can.
|
if you can.
|
||||||
- **There is no stable `Stream`/`AsyncIterator` interface yet.**
|
- **There is no stable `Stream`/`AsyncIterator` interface yet.**\
|
||||||
An `AsyncIterator` is, conceptually, an iterator that yields new items
|
An `AsyncIterator` is, conceptually, an iterator that yields new items
|
||||||
asynchronously. There is ongoing design work, but no consensus (yet).
|
asynchronously. There is ongoing design work, but no consensus (yet).
|
||||||
If you're using `tokio`, refer to [`tokio_stream`](https://docs.rs/tokio-stream/latest/tokio_stream/)
|
If you're using `tokio`, refer to [`tokio_stream`](https://docs.rs/tokio-stream/latest/tokio_stream/)
|
||||||
as your go-to interface.
|
as your go-to interface.
|
||||||
- **Be careful with buffering.**
|
- **Be careful with buffering.**\
|
||||||
It is often the cause of subtle bugs. Check out
|
It is often the cause of subtle bugs. Check out
|
||||||
["Barbara battles buffered streams"](https://rust-lang.github.io/wg-async/vision/submitted_stories/status_quo/barbara_battles_buffered_streams.html)
|
["Barbara battles buffered streams"](https://rust-lang.github.io/wg-async/vision/submitted_stories/status_quo/barbara_battles_buffered_streams.html)
|
||||||
for more details.
|
for more details.
|
||||||
- **There is no equivalent of scoped threads for asynchronous tasks**.
|
- **There is no equivalent of scoped threads for asynchronous tasks**.\
|
||||||
Check out ["The scoped task trilemma"](https://without.boats/blog/the-scoped-task-trilemma/)
|
Check out ["The scoped task trilemma"](https://without.boats/blog/the-scoped-task-trilemma/)
|
||||||
for more details.
|
for more details.
|
||||||
|
|
||||||
Don't let these caveats scare you: asynchronous Rust is being used effectively
|
Don't let these caveats scare you: asynchronous Rust is being used effectively
|
||||||
at _massive_ scale (e.g. AWS, Meta) to power foundational services.
|
at _massive_ scale (e.g. AWS, Meta) to power foundational services.\
|
||||||
You will have to master it if you're planning building networked applications
|
You will have to master it if you're planning building networked applications
|
||||||
in Rust.
|
in Rust.
|
||||||
|
|
|
@ -1,8 +1,8 @@
|
||||||
# Epilogue
|
# Epilogue
|
||||||
|
|
||||||
Our tour of Rust ends here.
|
Our tour of Rust ends here.\
|
||||||
It has been quite extensive, but by no means exhaustive: Rust is a language with
|
It has been quite extensive, but by no means exhaustive: Rust is a language with
|
||||||
a large surface area, and an even larger ecosystem!
|
a large surface area, and an even larger ecosystem!\
|
||||||
Don't let this scare you, though: there's **no need to learn everything**.
|
Don't let this scare you, though: there's **no need to learn everything**.
|
||||||
You'll pick up whatever is necessary to be effective in the domain
|
You'll pick up whatever is necessary to be effective in the domain
|
||||||
(backend, embedded, CLIs, GUIs, etc.) **while working on your projects**.
|
(backend, embedded, CLIs, GUIs, etc.) **while working on your projects**.
|
||||||
|
@ -34,21 +34,20 @@ way.
|
||||||
### Advanced material
|
### Advanced material
|
||||||
|
|
||||||
If you want to dive deeper into the language, refer to the [Rustonomicon](https://doc.rust-lang.org/nomicon/)
|
If you want to dive deeper into the language, refer to the [Rustonomicon](https://doc.rust-lang.org/nomicon/)
|
||||||
and ["Rust for Rustaceans"](https://nostarch.com/rust-rustaceans).
|
and ["Rust for Rustaceans"](https://nostarch.com/rust-rustaceans).\
|
||||||
The ["Decrusted" series](https://www.youtube.com/playlist?list=PLqbS7AVVErFirH9armw8yXlE6dacF-A6z) is another excellent
|
The ["Decrusted" series](https://www.youtube.com/playlist?list=PLqbS7AVVErFirH9armw8yXlE6dacF-A6z) is another excellent
|
||||||
resource to learn more about the internals of many of the most popular Rust libraries.
|
resource to learn more about the internals of many of the most popular Rust libraries.
|
||||||
|
|
||||||
### Domain-specific material
|
### Domain-specific material
|
||||||
|
|
||||||
If you want to use Rust for backend development,
|
If you want to use Rust for backend development,
|
||||||
check out ["Zero to Production in Rust"](https://zero2prod.com).
|
check out ["Zero to Production in Rust"](https://zero2prod.com).\
|
||||||
If you want to use Rust for embedded development,
|
If you want to use Rust for embedded development,
|
||||||
check out the [Embedded Rust book](https://docs.rust-embedded.org/book/).
|
check out the [Embedded Rust book](https://docs.rust-embedded.org/book/).
|
||||||
|
|
||||||
### Masterclasses
|
### Masterclasses
|
||||||
|
|
||||||
You can then find resources on key topics that cut across domains.
|
You can then find resources on key topics that cut across domains.\
|
||||||
For testing, check out
|
For testing, check out
|
||||||
["Advanced testing, going beyond the basics"](https://github.com/mainmatter/rust-advanced-testing-workshop).
|
["Advanced testing, going beyond the basics"](https://github.com/mainmatter/rust-advanced-testing-workshop).\
|
||||||
For telemetry, check out ["You can't fix what you can't see"](https://github.com/mainmatter/rust-telemetry-workshop).
|
For telemetry, check out ["You can't fix what you can't see"](https://github.com/mainmatter/rust-telemetry-workshop).
|
||||||
|
|
||||||
|
|
11
dprint.json
Normal file
11
dprint.json
Normal file
|
@ -0,0 +1,11 @@
|
||||||
|
{
|
||||||
|
"markdown": {
|
||||||
|
},
|
||||||
|
"toml": {
|
||||||
|
},
|
||||||
|
"excludes": [],
|
||||||
|
"plugins": [
|
||||||
|
"https://plugins.dprint.dev/markdown-0.17.0.wasm",
|
||||||
|
"https://plugins.dprint.dev/toml-0.6.1.wasm"
|
||||||
|
]
|
||||||
|
}
|
|
@ -4,5 +4,5 @@ version = "0.1.0"
|
||||||
edition = "2021"
|
edition = "2021"
|
||||||
|
|
||||||
[dev-dependencies]
|
[dev-dependencies]
|
||||||
static_assertions = "1.1.0"
|
|
||||||
common = { path = "../../../helpers/common" }
|
common = { path = "../../../helpers/common" }
|
||||||
|
static_assertions = "1.1.0"
|
||||||
|
|
|
@ -4,5 +4,5 @@ version = "0.1.0"
|
||||||
edition = "2021"
|
edition = "2021"
|
||||||
|
|
||||||
[dependencies]
|
[dependencies]
|
||||||
ticket_fields = { path = "../../../helpers/ticket_fields" }
|
|
||||||
thiserror = "1.0.59"
|
thiserror = "1.0.59"
|
||||||
|
ticket_fields = { path = "../../../helpers/ticket_fields" }
|
||||||
|
|
|
@ -4,5 +4,5 @@ version = "0.1.0"
|
||||||
edition = "2021"
|
edition = "2021"
|
||||||
|
|
||||||
[dependencies]
|
[dependencies]
|
||||||
ticket_fields = { path = "../../../helpers/ticket_fields" }
|
|
||||||
thiserror = "1.0.60"
|
thiserror = "1.0.60"
|
||||||
|
ticket_fields = { path = "../../../helpers/ticket_fields" }
|
||||||
|
|
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