Programming Techniques:Double Dispatch

From GDWiki

This article is a stub. You can help out by expanding it.

The following is an example of an implementation of double dispatch in C++.

   class A;
   class B;
   
   class Collidable
   {
   public:
       virtual void Collide( Collidable* x ) = 0;
       virtual void Collide( A* x ) = 0;
       virtual void Collide( B* x ) = 0;
   };
   
   class A : public Collidable
   {
   public:
       virtual void Collide( Collidable* x )
       {
           x->Collide( this );
       }
       virtual void Collide( A* a )
       {
           CollideAA( this, a ); // A-A
       }
       virtual void Collide( B* b )
       {
           CollideAB( this, b ); // A-B
       }
   };
   
   class B : public Collidable
   {
   public:
       virtual void Collide( Collidable* x )
       {
           x->Collide( this );
       }
       virtual void Collide( B* b )
       {
           CollideBB( this, b ); // B-B
       }
       virtual void Collide( A* a )
       {
           CollideAB( a, this ); // A-B
       }
   };
   
   void CollideAA( A* x, A* y )
   {
       // Do A-A collision
   }
   
   void CollideBB( B* x, B* y )
   {
       // Do B-B collision
   }
   
   void CollideAB( A* x, B* y )
   {
       // Do A-B collision
   }
   
   // Main collision function
   void Collide( Collidable* x, Collidable* y )
   {
       x->Collide( y );
   }