C++ named requirements: CopyInsertable (since C++11)

Specifies that an object of the type can be copy-constructed in-place 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*`
Expression	Definition
`v`	an expression denoting an lvalue of type `T` / constT, or an rvalue of type constT
`expr`	`std::allocator_traits<A>::construct(m, p, v)`

T is CopyInsertable into X if all following conditions are satisfied:

T is MoveInsertable into X.
expr is well-formed.
Evaluating expr does not change the value of v.
Right after the evaluation of expr, the value of v is equivalent to *p.

Notes

If A is std::allocator<T>, then this will call placement new, as by ::new((void*)p) T(v)(until C++20)std::construct_at(p, v)(since C++20).

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.

Defect reports

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

DR	Applied to	Behavior as published	Correct behavior
LWG 2177	C++11	evaluting `expr` did not have any postcondition	added
LWG 3957	C++11	`v` could denote an rvalue of type `T`	excluded

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