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@ -113,4 +113,3 @@ You can think of a type as a **tag** that the compiler attaches to every value i
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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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If leveraged correctly, types can prevent whole classes of runtime bugs.
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If leveraged correctly, types can prevent whole classes of runtime bugs.
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@ -14,4 +14,3 @@ It might not sound like much, but it'll give us a chance to cover a lot of Rust'
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Nailing the basics with a few exercises will get the language flowing under your fingers.
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Nailing the basics with a few exercises will get the language flowing under your fingers.
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When we move on to more complex topics, such as traits and ownership, you'll be able to focus on the new concepts
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When we move on to more complex topics, such as traits and ownership, you'll be able to focus on the new concepts
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without getting bogged down by the syntax or other trivial details.
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without getting bogged down by the syntax or other trivial details.
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@ -99,4 +99,3 @@ let message = if number < 5 {
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In the example above, each branch of the `if` evaluates to a string literal,
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In the example above, each branch of the `if` evaluates to a string literal,
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which is then assigned to the `message` variable.\
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which is then assigned to the `message` variable.\
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The only requirement is that both `if` branches return the same type.
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The only requirement is that both `if` branches return the same type.
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@ -9,4 +9,3 @@ So far you've learned:
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- How to execute conditional logic via comparisons and `if`/`else` expressions
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- How to execute conditional logic via comparisons and `if`/`else` expressions
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It looks like you're ready to tackle factorials!
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It looks like you're ready to tackle factorials!
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@ -16,4 +16,3 @@ To move forward you'll have to pick up several new Rust concepts, such as:
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- Memory management: stack, heap, pointers, data layout, destructors
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- Memory management: stack, heap, pointers, data layout, destructors
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- Modules and visibility
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- Modules and visibility
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- Strings
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- Strings
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@ -136,4 +136,3 @@ let is_open = Ticket::is_open(ticket);
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The function call syntax makes it quite clear that `ticket` is being used as `self`, the first parameter of the method,
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The function call syntax makes it quite clear that `ticket` is being used as `self`, the first parameter of the method,
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but it's definitely more verbose. Prefer the method call syntax when possible.
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but it's definitely more verbose. Prefer the method call syntax when possible.
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@ -112,4 +112,3 @@ where each name comes from and potentially introducing name conflicts.\
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Nonetheless, it can be useful in some cases, like when writing unit tests. You might have noticed
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Nonetheless, it can be useful in some cases, like when writing unit tests. You might have noticed
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that most of our test modules start with a `use super::*;` statement to bring all the items from the parent module
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that most of our test modules start with a `use super::*;` statement to bring all the items from the parent module
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(the one being tested) into scope.
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(the one being tested) into scope.
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@ -43,4 +43,3 @@ pub struct Configuration {
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`Configuration` is public, but you can only access the `version` field from within the same crate.
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`Configuration` is public, but you can only access the `version` field from within the same crate.
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The `active` field, instead, is private and can only be accessed from within the same module or one of its submodules.
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The `active` field, instead, is private and can only be accessed from within the same module or one of its submodules.
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@ -106,4 +106,3 @@ ticket.set_title("New title".into());
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ticket.set_description("New description".into());
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ticket.set_description("New description".into());
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ticket.set_status("In Progress".into());
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ticket.set_status("In Progress".into());
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```
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```
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@ -3,4 +3,3 @@
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We've covered a lot of foundational Rust concepts in this chapter.\
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We've covered a lot of foundational Rust concepts in this chapter.\
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Before moving on, let's go through one last exercise to consolidate what we've learned.
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Before moving on, let's go through one last exercise to consolidate what we've learned.
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You'll have minimal guidance this time—just the exercise description and the tests to guide you.
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You'll have minimal guidance this time—just the exercise description and the tests to guide you.
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@ -18,4 +18,3 @@ On top of traits as a concept, we'll also cover some of the key traits that are
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Since we'll be talking about conversions, we'll seize the opportunity to plug some of the "knowledge gaps"
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Since we'll be talking about conversions, we'll seize the opportunity to plug some of the "knowledge gaps"
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from the previous chapter—e.g. what is `"A title"`, exactly? Time to learn more about slices too!
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from the previous chapter—e.g. what is `"A title"`, exactly? Time to learn more about slices too!
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@ -96,4 +96,3 @@ impl PartialEq for MyType {
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}
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}
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}
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}
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```
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```
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@ -170,4 +170,3 @@ The rationale is the same as for [explicit type annotations on function paramete
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each function signature is a contract between the caller and the callee, and the terms must be explicitly stated.
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each function signature is a contract between the caller and the callee, and the terms must be explicitly stated.
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This allows for better error messages, better documentation, less unintentional breakages across versions,
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This allows for better error messages, better documentation, less unintentional breakages across versions,
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and faster compilation times.
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and faster compilation times.
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@ -114,4 +114,3 @@ If a method returns a `&String`, you're promising that there is heap-allocated U
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**matches exactly** the one you're returning a reference to.\
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**matches exactly** the one you're returning a reference to.\
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If a method returns a `&str`, instead, you have a lot more freedom: you're just saying that _somewhere_ there's a
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If a method returns a `&str`, instead, you have a lot more freedom: you're just saying that _somewhere_ there's a
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bunch of text data and that a subset of it matches what you need, therefore you're returning a reference to it.
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bunch of text data and that a subset of it matches what you need, therefore you're returning a reference to it.
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@ -89,4 +89,3 @@ Automatically converting types can make the code harder to read and understand.
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is defined on both `T` and `U`, which one will be called?
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is defined on both `T` and `U`, which one will be called?
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We'll examine later in the course the "safest" use cases for deref coercion: smart pointers.
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We'll examine later in the course the "safest" use cases for deref coercion: smart pointers.
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@ -77,4 +77,3 @@ All the types we've seen so far are `Sized`: `u32`, `String`, `bool`, etc.
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`str`, as we just saw, is not `Sized`.\
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`str`, as we just saw, is not `Sized`.\
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`&str` is `Sized` though! We know its size at compile time: two `usize`s, one for the pointer
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`&str` is `Sized` though! We know its size at compile time: two `usize`s, one for the pointer
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and one for the length.
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and one for the length.
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@ -138,4 +138,3 @@ In most cases, the target type is either:
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- Specified in the variable declaration with a type annotation (e.g. `let title: String = "A title".into();`)
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- Specified in the variable declaration with a type annotation (e.g. `let title: String = "A title".into();`)
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`.into()` will work out of the box as long as the compiler can infer the target type from the context without ambiguity.
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`.into()` will work out of the box as long as the compiler can infer the target type from the context without ambiguity.
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@ -105,4 +105,3 @@ struct MyType {
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The compiler implements `Clone` for `MyType` as you would expect: it clones each field of `MyType` individually and
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The compiler implements `Clone` for `MyType` as you would expect: it clones each field of `MyType` individually and
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then constructs a new `MyType` instance using the cloned fields.\
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then constructs a new `MyType` instance using the cloned fields.\
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Remember that you can use `cargo expand` (or your IDE) to explore the code generated by `derive` macros.
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Remember that you can use `cargo expand` (or your IDE) to explore the code generated by `derive` macros.
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@ -111,4 +111,3 @@ struct MyStruct {
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field: u32,
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field: u32,
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}
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}
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```
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```
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2 | #[derive(Clone, Copy)]
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2 | #[derive(Clone, Copy)]
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| ^^^^ `Copy` not allowed on types with destructors
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| ^^^^ `Copy` not allowed on types with destructors
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```
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```
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@ -25,4 +25,3 @@ A few guidelines to keep in mind:
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Before moving on, let's go through one last exercise to consolidate what we've learned.
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Before moving on, let's go through one last exercise to consolidate what we've learned.
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You'll have minimal guidance this time—just the exercise description and the tests to guide you.
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You'll have minimal guidance this time—just the exercise description and the tests to guide you.
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@ -13,4 +13,3 @@ We'll need to introduce a few more concepts along the way:
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- The `Error` trait, to mark error types
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- The `Error` trait, to mark error types
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- The `TryFrom` and `TryInto` traits, for fallible conversions
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- The `TryFrom` and `TryInto` traits, for fallible conversions
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- Rust's package system, explaining what's a library, what's a binary, how to use third-party crates
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- Rust's package system, explaining what's a library, what's a binary, how to use third-party crates
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```
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```
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`enum`, just like `struct`, defines **a new Rust type**.
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`enum`, just like `struct`, defines **a new Rust type**.
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```
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```
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The `_` pattern matches anything that wasn't matched by the previous patterns.
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The `_` pattern matches anything that wasn't matched by the previous patterns.
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}
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}
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}
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}
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```
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```
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Both `if let` and `let/else` are idiomatic Rust constructs.\
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Both `if let` and `let/else` are idiomatic Rust constructs.\
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Use them as you see fit to improve the readability of your code,
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Use them as you see fit to improve the readability of your code,
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but don't overdo it: `match` is always there when you need it.
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but don't overdo it: `match` is always there when you need it.
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```
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```
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Tuples are a convenient way of grouping values together when you can't be bothered to define a dedicated struct type.
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Tuples are a convenient way of grouping values together when you can't be bothered to define a dedicated struct type.
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Keep in mind, though, that panics exist. They aren't tracked by the type system, just like exceptions in other languages.
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Keep in mind, though, that panics exist. They aren't tracked by the type system, just like exceptions in other languages.
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But they're meant for **unrecoverable errors** and should be used sparingly.
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But they're meant for **unrecoverable errors** and should be used sparingly.
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Err(err) => eprintln!("Error: {}", err),
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Err(err) => eprintln!("Error: {}", err),
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}
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}
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```
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```
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}
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}
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}
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}
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```
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```
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while `Debug` provides a low-level representation that's more suitable to developers and service operators.\
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while `Debug` provides a low-level representation that's more suitable to developers and service operators.\
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That's why `Debug` can be automatically implemented using the `#[derive(Debug)]` attribute, while `Display`
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That's why `Debug` can be automatically implemented using the `#[derive(Debug)]` attribute, while `Display`
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**requires** a manual implementation.
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**requires** a manual implementation.
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@ -61,4 +61,3 @@ binary crate inside. If you want to create a library crate instead, you can use
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```bash
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```bash
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cargo new my-library --lib
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cargo new my-library --lib
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```
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```
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```
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```
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We've been using a few of these throughout the book to shorten our tests.
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We've been using a few of these throughout the book to shorten our tests.
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- `#[derive(thiserror::Error)]`: this is the syntax to derive the `Error` trait for a custom error type, helped by `thiserror`.
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- `#[derive(thiserror::Error)]`: this is the syntax to derive the `Error` trait for a custom error type, helped by `thiserror`.
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- `#[error("{0}")]`: this is the syntax to define a `Display` implementation for each variant of the custom error type.
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- `#[error("{0}")]`: this is the syntax to define a `Display` implementation for each variant of the custom error type.
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`{0}` is replaced by the zero-th field of the variant (`String`, in this case) when the error is displayed.
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`{0}` is replaced by the zero-th field of the variant (`String`, in this case) when the error is displayed.
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Just like `From` and `Into`, `TryFrom` and `TryInto` are dual traits.\
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Just like `From` and `Into`, `TryFrom` and `TryInto` are dual traits.\
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If you implement `TryFrom` for a type, you get `TryInto` for free.
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If you implement `TryFrom` for a type, you get `TryInto` for free.
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You can use the `?` operator to shorten your error handling code significantly.\
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You can use the `?` operator to shorten your error handling code significantly.\
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In particular, the `?` operator will automatically convert the error type of the fallible operation into the error type
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In particular, the `?` operator will automatically convert the error type of the fallible operation into the error type
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of the function, if a conversion is possible (i.e. if there is a suitable `From` implementation)
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of the function, if a conversion is possible (i.e. if there is a suitable `From` implementation)
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