Detail at: https://en.cppreference.com/w/cpp/utility/hash

Hash function for Pair<T1, T2>

struct PairHash {
	template<class T1, class T2>
	std::size_t operator()(std::pair<T1, T2> const & p) const noexcept {
		std::size_t hash1 = std::hash<T1>{}(p.first);
		std::size_t hash2 = std::hash<T2>{}(p.second);		
		return hash1 ^ (hash2 << 1);
	};	
};