template <class T1, class T2>
constexpr bool operator==(const pair<T1, T2>& x, const pair<T1, T2>& y);
Returns: x.first == y.first && x.second == y.second.
template <class T1, class T2>
constexpr bool operator<(const pair<T1, T2>& x, const pair<T1, T2>& y);
Returns: x.first < y.first || (!(y.first < x.first) && x.second < y.second).
template <class T1, class T2>
constexpr bool operator!=(const pair<T1, T2>& x, const pair<T1, T2>& y);
Returns: !(x == y).
template <class T1, class T2>
constexpr bool operator>(const pair<T1, T2>& x, const pair<T1, T2>& y);
Returns: y < x.
template <class T1, class T2>
constexpr bool operator>=(const pair<T1, T2>& x, const pair<T1, T2>& y);
Returns: !(x < y).
template <class T1, class T2>
constexpr bool operator<=(const pair<T1, T2>& x, const pair<T1, T2>& y);
Returns: !(y < x).
template<class T1, class T2> void swap(pair<T1, T2>& x, pair<T1, T2>& y)
noexcept(noexcept(x.swap(y)));
Effects: As if by x.swap(y).
Remarks: This function shall not participate in overload resolution unless is_swappable_v<T1> is true and is_swappable_v<T2> is true.
template <class T1, class T2>
constexpr pair<V1, V2> make_pair(T1&& x, T2&& y);
Returns: pair<V1, V2>(std::forward<T1>(x), std::forward<T2>(y)), where V1 and V2 are determined as follows: Let Ui be decay_t<Ti> for each Ti. Then each Vi is X& if Ui equals reference_wrapper<X>, otherwise Vi is Ui.
[ Example: 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 ]