#include <iostream>

struct TestData {
	friend bool operator < (const TestData&, const TestData&);
	TestData(int keyField) : keyField_(keyField) {}
private:
	int keyField_;
};

bool operator < (const TestData& lhs, const TestData& rhs)
{
	return lhs.keyField_ < rhs.keyField_;
}

int main() {
	TestData a{1}, b{2};
	std::cout << (a < b) << '\n';
	return 0;
}