Difference between revisions of "cpp/named req/EmplaceConstructible"
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| − | If {{ttb|X}} is not allocator-aware, the term is defined as if {{ttb|A}} were {{lc|std::allocator<T>}}, except that no allocator object needs to be created, and user-defined specializations of {{lc|std::allocator}} are not instantiated. | + | If {{ttb|X}} is not allocator-aware or is a {{lc|std::basic_string}} specialization, the term is defined as if {{ttb|A}} were {{lc|std::allocator<T>}}, except that no allocator object needs to be created, and user-defined specializations of {{lc|std::allocator}} are not instantiated. |
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| + | ===Notes=== | ||
| + | Although it is required that customized {{tt|construct}} is used when constructing elements of {{lc|std::basic_string}} until C++23, all implementations only used the default mechanism. The requirement is corrected by {{wg21|P1072R10}} to match existing practice. | ||
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Latest revision as of 23:36, 29 October 2021
Specifies that an object of the type can be constructed from a given set of arguments in uninitialized storage by a given allocator.
[edit] Requirements
The type T is EmplaceConstructible into the Container X (whose value_type is identical to T) from the arguments args if, given
A
|
an allocator type |
m
|
an lvalue of type A
|
p
|
the pointer of type T* prepared by the container
|
args
|
zero or more arguments |
where X::allocator_type is identical to std::allocator_traits<A>::rebind_alloc<T>,
the following expression is well-formed:
std::allocator_traits<A>::construct(m, p, args);
If X is not allocator-aware or is a std::basic_string specialization, the term is defined as if A were std::allocator<T>, except that no allocator object needs to be created, and user-defined specializations of std::allocator are not instantiated.
[edit] Notes
Although it is required that customized construct is used when constructing elements of std::basic_string until C++23, all implementations only used the default mechanism. The requirement is corrected by P1072R10 to match existing practice.
[edit] See also
| CopyInsertable | |
| MoveInsertable |
