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

Specifies that an object of the type can be constructed from a given set of arguments in uninitialized storage by a given allocator.

Requirements​

The type T is MoveInsertable into the container X whose value_type is identical to T from the arguments args if given

  • A an allocator type
  • m an lvalue of type A
  • p the pointer of type T* prepared by the container
  • args zero or more arguments

where X::allocator_type is identical to std::allocator_traits<A>::rebind_alloc<T>,

the following expression is well-formed:

std::allocator_traits<A>::construct(m, p, args);

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​

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.

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

Specifies that an object of the type can be constructed from a given set of arguments in uninitialized storage by a given allocator.

Requirements​

The type T is MoveInsertable into the container X whose value_type is identical to T from the arguments args if given

  • A an allocator type
  • m an lvalue of type A
  • p the pointer of type T* prepared by the container
  • args zero or more arguments

where X::allocator_type is identical to std::allocator_traits<A>::rebind_alloc<T>,

the following expression is well-formed:

std::allocator_traits<A>::construct(m, p, args);

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​

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.