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[utility.exchange]

22 General utilities library [utilities]

22.2 Utility components [utility]

22.2.3 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>