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WIP updating sections about unrestricted unions

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Frank B. Brokken 2012-02-22 22:24:39 +01:00
parent fc3bf88091
commit 3d76b1b80a
1 changed files with 2 additions and 57 deletions
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59
yo/containers/unrestricted.yo
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@ -206,37 +206,6 @@ initializations that would have been used if the union fields were members
become statements using the placement new operator in the bodies of the become statements using the placement new operator in the bodies of the
constructors. constructors.
>>>>>>>>>>>>>>>>>>>> WIP
likewise. (or move)
how to initialize constructor's member initialization
section).already exists by the time the me These are implemented by calling
the appropriate constructor
Now for the destructor: the destructor should call the appropriate
destructor of the currently active data fields having non-trivial
destructors. So, in our tt(Union) union the tt(u_int) field can be
ignored. The destructor now has an easy job: depending on the (any) field's
tt(first) data member it picks the right destructor. Since the data fields
weren't dynamically allocated, we don't use tt(delete). Instead we use the
procedure previously encountered with em(placement new), explicitly calling
the field's destructor where needed:
verb(
Union::~Union()
{
switch (u_int.first)
{
case 2:
u_complex.second.~complex<double>();
break;
case 3:
u_string.second.~string();
break;
}
}
)
What about changing fields? Once an unrestricted union has received its What about changing fields? Once an unrestricted union has received its
value it keeps that variant until used otherwise. That's in line with the value it keeps that variant until used otherwise. That's in line with the
traditional union. But to change the interpretation of an unrestricted union's traditional union. But to change the interpretation of an unrestricted union's
@ -244,33 +213,9 @@ class-type field we must make sure that the destructor of that
class type field is first called. To do that smoothly we need class type field is first called. To do that smoothly we need
tt(operator=). tt(operator=).
Once again we encounter a complication: unrestricted unions don't even FBB WIP ==================================================================
have a default copy constructor. That's again understandable: which field
should be initialized by the copy constructor? But as we've implemented a
means of determining the currently active field the problem is easily solved,
once we realize that the memory in the destination object is waiting to be
used and that placement new is the tool to perform the initialization
with. Here is tt(Union)'s copy constructor:
verb(
Union::Union(Union const &other)
{
switch (other.u_int.first)
{
case 1:
new (&u_int) std::pair<int, int>(other.u_int);
break;
case 2:
new (&u_complex)
std::pair<int, complex<double>>(other.u_complex);
break;
case 3:
new (&u_string) std::pair<int, string>(other.u_string);
break;
}
}
)
Preparing for tt(operator=) we first implement tt(Union::swap), swapping Preparing for tt(operator=) we first implement tt(MultiData::swap), swapping
the current and another tt(Union) object, using fast swapping as discussed in the current and another tt(Union) object, using fast swapping as discussed in
section ref(FSWAP): section ref(FSWAP):
verb( verb(