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

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< cpp‎ | named req

Specifies that an object of the type can be constructed into uninitialized storage from an rvalue of that type by a given allocator.

### Requirements

The type `T` is MoveInsertable 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
`rv` | rvalue expression of type `T`

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, rv);

And after evaluation, the value of `*p` is equivalent to the value formerly held by `rv` (`rv` remains valid, but is in an unspecified state.)

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

If `A` is std::allocator<T>, then this will call placement-new, as by ::new((void*)p) T(rv) (until C++20)std::construct_at(p, rv) (since C++20). This effectively requires `T` to be move constructible.

If std::allocator<T> or a similar allocator is used, a class does not have to implement a move constructor to satisfy this type requirement: a copy constructor that takes a const T& argument can bind rvalue expressions. If a MoveInsertable class implements a move constructor, it may also implement move semantics to take advantage of the fact that the value of `rv` after construction is unspecified.

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

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