From cppreference.com
Specifies that an object of the type can be constructed into uninitialized storage from an rvalue of that type by a given allocator.
Requirements
Given the following types, values and expressions:
Type Definition Tan object type Aan allocator type Xa container type satisfying all following conditions: X::value_type is the same as T.
X::allocator_type is the same as std::allocator_traits<A>::rebind_alloc<T>.
Value Definition man lvalue of type Apa pointer of type T*Expression Definition rvan expression denoting an rvalue of type Texprstd::allocator_traits<A>::construct(m,p,rv)T is MoveInsertable into X if all following conditions are satisfied:
expr is well-formed.
Right after the evaluation of expr, the value of *p is equivalent to the value of rv before the evaluation.
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
to satisfy this type requirement: a
that takes a constT& argument can bind rvalue expressions. If a MoveInsertable class implements a move constructor, it may also implement
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
until C++23, all implementations only used the default mechanism. The requirement is corrected by
to match existing practice.
Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
DR Applied to Behavior as published Correct behavior
C++11 evaluting expr did not have any postcondition added See also