C++ named requirements: DefaultInsertable

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C++ named requirements

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


The type T is DefaultInsertable into the Container X whose value_type is identical to T if, given

A an allocator type
m an lvalue of type A
p the pointer of type T* prepared by the container

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);

If X is not allocator-aware, 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.


By default, this will call placement-new, as by ::new((void*)p) T() (that is, value-initialize the object pointed to by p). If value-initialization is undesirable, for example, if the object is of non-class type and zeroing out is not needed, it can be avoided by providing a custom Allocator::construct.

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