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

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< cpp‎ | named req

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 EmplaceConstructible 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.

### See also

CopyInsertable
MoveInsertable

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