#include <iostream>
#include <string>

using std::operator""s;

template<class T> concept Addable = requires (T t) { t + t; };

template<class T> void test(T a, T b)
{
	Addable auto c = a + b;
	std::cout << a << " + " << b << " = " << c << std::endl;
}

int main()
{
	test(     1,      2);
	test("abc"s, "xyz"s);
}