C++ named requirements: CopyInsertable (since C++11) (original) (raw)
Specifies that an object of the type can be copy-constructed in-place by a given allocator.
[edit] 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 / const T, or an rvalue of type const T |
| expr | std::allocator_traits<A>::construct(m, p, v) |
T is CopyInsertable into X if all following conditions are satisfied:
Tis MoveInsertable intoX.- 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.
[edit] 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.
[edit] 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 |