C / C++ / MFC

class CommandVisitor
{
  // as many overloads for visits as there are commands 
  virtual void visit(Command1&);
  virtual void visit(Command2&);
  ...
  virtual void visit(Commandn&);
}

class Command
{
  ... // as before
  virtual void accept(CommandVisitor&)=0;
}

class Command2: public Command
{
  void accept(CommandVisitor& visitor)
  {
    visitor.visit(*this); // calls the overload of CommandVisitor::visit for Command2
  }
}

class Protocol1:public Visitor
{
  string result;
  string toString(Command& command)
  {
    // let the visitor magic do the matching
    command.accept(*this);
    // take the result
    return result;
  }
  void visit(Command1 &command)
  {
    result=...; //stuff for Command1.
  }
  ...
  void visit(Commandn &command)
  {
    result=...; //stuff for Commandn.
  }
}