Multiple Instances? [question] about interpreter HOT 3 CLOSED

interpreter.h  

  explicit 
  Interpreter();
  ~Interpreter();

  Interpreter(const Interpreter&);
  Interpreter& operator=(const Interpreter&);
  .
  .

interpreter.cpp

  Interpreter::Interpreter() {
    m_d = new InterpreterImpl();
  }
  Interpreter::~Interpreter() {
    delete m_d;
  }
  Interpreter::Interpreter(const Interpreter& other) {
    m_d = new InterpreterImpl();
    *m_d = *other.m_d;
  }
  Interpreter& Interpreter::operator=(const Interpreter& other){
    if (this->m_d != other.m_d)   
      *m_d = *other.m_d;  
    return *this;
  }
  .
  .

class Programmer {
public:
  Programmer() {
    cmdline.addOperator("=", [](string& leftOpd, string& rightOpd) ->string {
      leftOpd = rightOpd;
      return leftOpd;
    }, 10);
    
    cmdline.addFunction("summ", [](const vector<string>& args) ->string {
      string res;
      for (auto& v : args) {
        res += v;
      }
      return res;
    });
  }
  Interpreter cmdline;
};

class t_user {
public:
  std::string name = "root";
  Programmer programmer; // each user has own programmer / interpreter / environment    
};

std::vector<t_user> Users;

void main(void) {

  t_user  tmp_user;
  tmp_user.name = "user1";
  Users.push_back(tmp_user);  // add a t_user to Users

  // Users[0] we just pushed
  std::string input = "$a = summ(1, 2);";
  auto res = Users[0].programmer.cmdline.cmd(input);   // <------- complains here

  res; // 12
}