# C++ named requirements: Erasable (since C++11)

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< cpp‎ | named req

Specifies that an object of the type can be destroyed by a given Allocator.

### Requirements

Given the following types, values and expressions:

Type | Definition
`T` | an object type
`A` | an allocator type

`X`

a container type satisfying all following conditions:

- `X::value_type` is the same as `T`.
- `X::allocator_type` is the same as std::allocator_traits <A>::rebind_alloc<T>.

Value | Definition
m | an lvalue of type `A`
p | a pointer of type `T*`

If the expression std::allocator_traits <A>::destroy(m, p) is well-formed, `T` is Erasable from `X`.

### Notes

All standard library containers require that their value types satisfy 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.

### Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR | Applied to | Behavior as published | Correct behavior
--- | --- | --- | ---
N3346 | C++11 | there was no requirement to specify whether a type whose objects can be destroyed using allocators | added the requirement

### See also

CopyInsertable
MoveInsertable
EmplaceConstructible
Destructible

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