hash_func & key_equal of std::unordered_map

x.cc

#include <cstdio>
#include <cstdlib>
#include <iostream>
#include <string>
#include <unordered_map>

struct Eq {
	bool operator()(int i, int j) const
	{
		return std::abs(i) == std::abs(j);
	}
};

int main()
{
	std::unordered_map<int, std::string, std::hash<int>, Eq> m = {
		{1, "one"},
		{2, "two"},
		{3, "thee"}
	};
	for (auto i : {-1, -2, -3}) {
		auto it = m.find(i);
		if (it != m.end())
			std::cout << "found: " << it->second << std::endl;
	}
	return EXIT_SUCCESS;
}