Defined in header <utility> (1) template< size_t N, class T1, class T2 >
typename std::tuple_element<I, std::pair<T1,T2> >::type&
get( pair<T1, T2>& p ); (since C++11) (until C++14) template< size_t N, class T1, class T2 >
constexpr std::tuple_element_t<I, std::pair<T1,T2> >&
get( pair<T1, T2>& p ); (since C++14) (2) template< size_t N, class T1, class T2 >
const typename std::tuple_element