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    cpp/named req/CopyInsertable: Difference between revisions

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    Specifies that an instance of the type can be copy-constructed in-place by a given allocator.
    Specifies that an of the type can be copy-constructed in-place by a given allocator.


    ===Requirements===
    ===Requirements===

    Latest revision as of 01:53, 7 November 2024

     
    C++
     
    C++ named requirements
     

    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 / 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:

    • 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