Pairs
With std::pair, you can build pairs of arbitrary types. The class template std::pair needs the header <utility>. std::pair has a default, copy and move constructor. Pair objects can be swapped: std::swap(pair1, pair2).
Pairs will often be used in the C++ library. For example, the function std::max returns its result as a pair, the associative container std::map, std::unordered_map, std::multimap and std::unordered_multimap manage their key/value association in pairs.
To get the elements of a pair p, you can either access it directly or via an index. So, with p.first or std::get<0>(p) you get the first, with p.second or `std::get<1>(p) you get the second element of the pair.
Pairs support the comparison operators ==, !=, <, >, <= and >=. If you compare two pairs for identity, at first the members pair1.first and pair2.first will be compared and then pair1.second and pair2.second. The same strategy holds for the other comparison operators.
