Difference between revisions of "cpp/named req/Erasable"
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| − | If {{ttb|X}} is not allocator-aware | + | If {{ttb|X}} is not allocator-aware or is a {{lc|std::basic_string}} specialization, the term is defined as if {{ttb|A}} were {{c|std::allocator<T>}}, except that no allocator object needs to be created, and user-defined specializations of {{lc|std::allocator}} are not instantiated. |
===Notes=== | ===Notes=== | ||
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With the default allocator, this requirement is equivalent to the validity of {{c|std::destroy_at(p)}}, which accepts class types with accessible destructors and all scalar types, as well as arrays thereof. | With the default allocator, this requirement is equivalent to the validity of {{c|std::destroy_at(p)}}, which accepts class types with accessible destructors and all scalar types, as well as arrays thereof. | ||
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| + | Although it is required that customized {{tt|destroy}} is used when destroying 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. | ||
===See also=== | ===See also=== | ||
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{{dsc end}} | {{dsc end}} | ||
| − | {{langlinks|es|ja|zh}} | + | {{langlinks|de|es|ja|ru|zh}} |
Revision as of 23:37, 29 October 2021
Specifies that an object of the type can be destroyed by a given Allocator.
Requirements
The type T is Erasable from the Container X whose value_type is identical to T if, given
A
|
an allocator type |
m
|
an lvalue of type A
|
p
|
the pointer of type T* prepared by the container
|
where X::allocator_type is identical to std::allocator_traits<A>::rebind_alloc<T>,
the following expression is well-formed:
std::allocator_traits<A>::destroy(m, p);
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.
Notes
All standard library containers require that their element type satisfies Erasable.
|
With the default allocator, this requirement is equivalent to the validity of p->~T(), which accepts class types with accessible destructors and all scalar types, but rejects array types, function types, reference types, and void. |
(until C++20) |
|
With the default allocator, this requirement is equivalent to the validity of std::destroy_at(p), which accepts class types with accessible destructors and all scalar types, as well as arrays thereof. |
(since C++20) |
Although it is required that customized destroy is used when destroying 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.
See also
| CopyInsertable | |
| MoveInsertable | |
| EmplaceConstructible | |
| Destructible |
