< cpp‎ | utility‎ | optional
template< class... Args >
T& emplace( Args&&... args );
(since C++17)
template< class U, class... Args >
T& emplace( std::initializer_list<U> ilist, Args&&... args );
(since C++17)

Constructs the contained value in-place. If *this already contains a value before the call, the contained value is destroyed by calling its destructor.

1) Initializes the contained value by direct-initializing (but not direct-list-initializing) with std::forward<Args>(args)... as parameters.
2) Initializes the contained value by calling its constructor with ilist, std::forward<Args>(args)... as parameters. This overload only participates in overload resolution if std::is_constructible<T, std::initializer_list<U>&, Args&&...>::value is true.


args... - the arguments to pass to the constructor
ilist - the initializer list to pass to the constructor
Type requirements
T must be constructible from Args... for overload (1)
T must be constructible from std::initializer_list and Args... for overload (2)

Return value

A reference to the new contained value.


Any exception thrown by the selected constructor of T. If an exception is thrown, *this does not contain a value after this call (the previously contained value, if any, had been destroyed).

See also

assigns contents
(public member function)