#include <functional>
 #include <iostream>
 #include <string>

 void invokeMe(std::string& s){
   std::cout << s << ": not const " << std::endl;
 }

 void invokeMe(const std::string& s){
   std::cout << s << ": const " << std::endl;
 }

 template <typename T>
 void doubleMe(T t){
   t *=2;
 }

 int main(){

   std::cout << std::endl;

   std::string s{"string"};

   invokeMe(std::ref(s));
   invokeMe(std::cref(s));

   std::cout << std::endl;

   int i=1;
   std::cout << "i: " << i << std::endl;

   doubleMe(i);
   std::cout << "doubleMe(i): " << i << std::endl;

   doubleMe(std::ref(i));
   std::cout << "doubleMe(std::ref(i)): " << i << std::endl;

   std::cout << std::endl;

 }