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

 class Bad{
 public:
   Bad(std::string& s):message(s){}
 private:
   std::string& message;
 };

 class Good{
 public:
   Good(std::string& s):message(s){}
   std::string getMessage(){
     return message.get();
   }
   void changeMessage(std::string s){
     message.get()= s;
   }
 private:
   std::reference_wrapper<std::string> message;
 };

 int main(){

   std::cout << std::endl;

   std::string bad1{"bad1"};
   std::string bad2{"bad2"};

   Bad b1(bad1);
   Bad b2(bad2);
   //b1= b2;

   std::string good1{"good1"};
   std::string good2{"good2"};

   Good g1(good1);
   Good g2(good2);
   std::cout << "g1.getMessage(): " << g1.getMessage() << std::endl;
   std::cout << "g2.getMessage(): " << g2.getMessage() << std::endl;

   std::cout << std::endl;

   std::cout << "g2= g1" << std::endl;
   g2= g1;
   std::cout << "g1.getMessage(): " << g1.getMessage() << std::endl;
   std::cout << "g2.getMessage(): " << g2.getMessage() << std::endl;

   std::cout << std::endl;

   g1.changeMessage("veryGood");
   std::cout << "g1.changeMessage(\"veryGood\")" << std::endl;
   std::cout << "g1.getMessage(): " << g1.getMessage() << std::endl;
   std::cout << "g2.getMessage(): " << g2.getMessage() << std::endl;

   std::cout << std::endl;

 }