20 General utilities library [utilities]

20.2 Utility components [utility]

20.2.3 exchange [utility.exchange]

template<class T, class U = T> constexpr T exchange(T& obj, U&& new_val) noexcept(see below);
Effects: Equivalent to: T old_val = std::move(obj); obj = std::forward<U>(new_val); return old_val;
Remarks: The exception specification is equivalent to: is_nothrow_move_constructible_v<T> && is_nothrow_assignable_v<T&, U>