std::expected<T,E>::emplace

< cpp‎ | utility‎ | expected

T is not cv void
template< class... Args > constexpr T& emplace( Args&&... args ) noexcept;	(1)	(since C++23)
template< class U, class... Args > constexpr T& emplace( std::initializer_list<U>& il, Args&&... args ) noexcept;	(2)	(since C++23)
T is cv void
constexpr void emplace() noexcept;	(3)	(since C++23)

Constructs an expected value in-place. After the call, has_value() returns true.

1) Destroys the contained value, then initializes the expected value contained in *this as if by direct-initializing an object of type T from the arguments std::forward<Args>(args).... This overload participates in overload resolution only if std::is_nothrow_constructible_v<T, Args...> is true.

2) Destroys the contained value, then initializes the expected value contained in *this as if by direct-initializing an object of type T from the arguments il, std::forward<Args>(args).... This overload participates in overload resolution only if std::is_nothrow_constructible_v<T, std::initializer_list<U>&, Args...> is true.

3) If *this contains an unexpected value, destroys that value.

Parameters

args...	-	the arguments to pass to the constructor
il	-	the initializer list to pass to the constructor

Return value

A reference to the new contained value.

Exceptions

noexcept specification:

noexcept

Notes

If the construction of T is potentially-throwing, this function is not defined. In this case, it is the responsibility of the user to create a temporary and move or copy it.

Example