Double dispatch/multimethods in C++

Question

I have a question on C++ double dispatch. In the code below, I want the results from the second set to match the results from the first set.

I don\'t know the actua

Answer 1

Thank you so much. This solved my problem and I understand what double dispatch means! Here is the complete code for posterity (somebody please teach me how to get the formatting right):

#include 
using namespace std;

class BaseClass;
class Derived1;
class Derived2;
class Derived3;

class Processor {
public:
       Processor(){}
       virtual void processObj(BaseClass* bc);
       virtual void processObj(Derived1* d1);
       virtual void processObj(Derived2* d2);
};


class BaseClass{
public:
       BaseClass(){}
       virtual void ProcessThis(Processor &p) { p.processObj(this); }
       virtual void myFunction(){cout << "base myFunction called" << endl;}
};

class Derived1: public BaseClass{
public:
       Derived1():BaseClass(){}
       void ProcessThis(Processor &p) { p.processObj(this); }
       void myFunction(){cout << "Derived1 myFunction called" << endl;}
};

class Derived2: public BaseClass{
public:
       Derived2():BaseClass(){}
       void ProcessThis(Processor &p) { p.processObj(this); }
       void myFunction(){cout << "Derived2 myFunction called" << endl;}
};

class Derived3: public BaseClass{
public:
       Derived3():BaseClass(){}
       void ProcessThis(Processor &p) { p.processObj(this); }
       void myFunction(){cout << "Derived3 myFunction called" << endl;}

};

void Processor::processObj(BaseClass* bc){cout << "got a base object" << endl; bc->myFunction();}
void Processor::processObj(Derived1* d1){cout << "got a derived1 object" << endl; d1->myFunction();}
void Processor::processObj(Derived2* d2){cout << "got a derived2 object" << endl; d2->myFunction(); }


int main() {
   BaseClass *bcp=new BaseClass();
   Derived1 *dc1p=new Derived1();   
   Derived2 *dc2p=new Derived2();
   Derived3 *dc3p=new Derived3();

   Processor p;//can also use Processor* p = new Processor()

   //first set results

   bcp->ProcessThis(p);
   dc1p->ProcessThis(p);
   dc2p->ProcessThis(p);
   dc3p->ProcessThis(p);

   BaseClass *bcp1=bcp;
   BaseClass *dc1p1=dc1p;   
   BaseClass *dc2p1=dc2p;
   BaseClass *dc3p1=dc3p;

   //second set results

   bcp1->ProcessThis(p);
   dc1p1->ProcessThis(p);
   dc2p1->ProcessThis(p);
   dc3p1->ProcessThis(p);

   Processor p2;
   bcp1->ProcessThis(p2);
   dc1p1->ProcessThis(p2);
   dc2p1->ProcessThis(p2);
   dc3p1->ProcessThis(p2);

   return 0;
}