[utility.swap]

template<class T>
  constexpr void swap(T& a, T& b) noexcept(see below);

Constraints: is_move_constructible_v<T> is true and is_move_assignable_v<T> is true.

Preconditions: Type T meets the Cpp17MoveConstructible (Table 31) and Cpp17MoveAssignable (Table 33) requirements.

Remarks: The exception specification is equivalent to: is_nothrow_move_constructible_v<T> && is_nothrow_move_assignable_v<T>

template<class T, size_t N>
  constexpr void swap(T (&a)[N], T (&b)[N]) noexcept(is_nothrow_swappable_v<T>);

Preconditions: a[i] is swappable with ([swappable.requirements]) b[i] for all i in the range [0, N).

Effects: As if by swap_ranges(a, a + N, b).

22 General utilities library [utilities]