22 General utilities library [utilities]

22.3 Pairs [pairs]

22.3.3 Specialized algorithms [pairs.spec]

template<class T1, class T2, class U1, class U2>
  constexpr bool operator==(const pair<T1, T2>& x, const pair<U1, U2>& y);

Constraints: x.first == y.first and x.second == y.second are valid expressions and each of decltype(x.first == y.first) and decltype(x.second == y.second) models boolean-
testable.

Returns: x.first == y.first && x.second == y.second.

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template<class T1, class T2, class U1, class U2>
  constexpr common_comparison_category_t<synth-three-way-result<T1, U1>,
                                         synth-three-way-result<T2, U2>>
    operator<=>(const pair<T1, T2>& x, const pair<U1, U2>& y);

Effects: Equivalent to: if (auto c = synth-three-way(x.first, y.first); c != 0) return c; return synth-three-way(x.second, y.second);

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template<class T1, class T2>
  constexpr void swap(pair<T1, T2>& x, pair<T1, T2>& y) noexcept(noexcept(x.swap(y)));
template<class T1, class T2>
  constexpr void swap(const pair<T1, T2>& x, const pair<T1, T2>& y) noexcept(noexcept(x.swap(y)));

Constraints:

(4.1)
For the first overload, is_swappable_v<T1> is true and is_swappable_v<T2> is true.
(4.2)
For the second overload, is_swappable_v<const T1> is true and is_swappable_v<const T2> is true.

Effects: Equivalent to x.swap(y).

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template<class T1, class T2>
  constexpr pair<unwrap_ref_decay_t<T1>, unwrap_ref_decay_t<T2>> make_pair(T1&& x, T2&& y);

Returns: pair<unwrap_ref_decay_t<T1>, unwrap_ref_decay_t<T2>>(std::forward<T1>(x), std::forward<T2>(y))

[Example 1:

In place of: return pair<int, double>(5, 3.1415926); // explicit types a C++ program may contain: return make_pair(5, 3.1415926); // types are deduced

— end example]