member_hash.cpp

#include <unordered_map>

namespace std {
	template <class T>
	struct member_hash {
		std::size_t operator()(const T& t) const {
			return t.hash();
		}
	};

	template <class Key, class Value>
	using unordered_map_member_hash = std::unordered_map<Key, Value, member_hash<Key>>;
}

struct Vertex {
	std::size_t hash() const {
		return 1337;
	}
};

struct Dupa {

};

int main() {
	std::unordered_map_member_hash<Vertex, Dupa> m;
}