Emplaces a new value in the optional, destroying the current one if the optional is engaged. Synopsis Declared in <beman/optional/optional.hpp> template<class U> requires (std::is_constructible_v<T&, U> && !detail::reference_constructs_from_temporary_v<T&, U>) constexpr T& emplace(U&& u) noexcept(std::is_nothrow_constructible_v<T &, U>); Description Constructs the contained value from u if it is convertible to T&. Return Value T& Template Parameters Name Description U The type of the value to emplace. Parameters Name Description u The value to emplace.