#include <iostream>
#include <string>
#include <vector>


struct in 
{
 std::vector<std::string> vec_str;
 void add_strings(){}

 template<typename T, typename... Args>
 void add_strings(T value, Args... args) {	
 	vec_str.push_back(value);
 	add_strings(args...);
 }
	
 template<typename... Args>
 in(Args... args) { 
 	add_strings(args...);
 }
};

bool operator==(std::string const& str, in const& val) {
 	for(auto &i : val.vec_str) {
 		if(i == str)
 			return true;
 	}
 	return false;	
}
// -----------------------------------------------------

int main(void) 
{
	std::string lang, country = "GB";

	if (country == in ("US","GB","AU")) {
		lang="en";
	}

	std::cout << "lang = " << lang << std::endl;

	return 0;
}