# C++ concepts: DefaultInsertable

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< cpp‎ | concept

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

### Requirements

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.

### Notes

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.

### See Also

`DefaultConstructible`
`CopyInsertable`
`MoveInsertable`
`EmplaceConstructible`
`Erasable`

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