Re: Double dispatch (makes no sense!)

saneman wrote:
> I am trying to use double dispatch in the below code:
> 
> #include <iostream>
> 
> class Box;
> class Sphere;
> 
> 
> class geometry_type
> {
> public:
>   virtual void haps(geometry_type* other)=0;
>   virtual void collideWith(Box* other)=0;
>   virtual void collideWith(Sphere* other) = 0;
> };
> 
> class Box : public geometry_type
> {
> public :
>   Box() {}
> 
>   virtual void haps(geometry_type* other)
>   {
>         other->collideWith(this);
>   }
> 
>   virtual void collideWith(Sphere* other) {
>     std::cout << "Sphere collision with Sphere" << std::endl;
>   }
> 
>   virtual void collideWith(Box* other) {
>     std::cout << "Box collision with Box" << std::endl;
>   }
> 
> 
> };
> 
> class Sphere : public geometry_type
> {
> public :
>   Sphere() {}
> 
>   virtual void haps(geometry_type* other)
>   {
>         other->collideWith(this);
>   }
> 
>   virtual void collideWith(Sphere* other) {
>     std::cout << "Sphere collision with Sphere" << std::endl;
>   }
> 
>   virtual void collideWith(Box* other) {
>     std::cout << "Sphere collision with Box" << std::endl;
>   }
> 
> 
> };
> 
> 
> void narrow_phase(geometry_type* G1, geometry_type* G2)
> {
>   G1->haps(G2);
> }
> 
> int main()
> {
>   Box* BoxA       = new Box();
>   Sphere* SphereA = new Sphere();
> 
>   BoxA->collideWith(BoxA);
>   SphereA->collideWith(BoxA);
> 
>   // Should print box collide with box.
>   narrow_phase(BoxA, BoxA);
> 
>   // Should print sphere collide with box.
>   narrow_phase(SphereA, BoxA);
> 
>   // Should print box collide with sphere.
>   narrow_phase(BoxA, SphereA);
> 
>   return 0;
> 
> }
> 
> 
> But when I run main I get:
> 
> Box collision with Box
> Sphere collision with Box
> Box collision with Box
> Sphere collision with Sphere
> Sphere collision with Box
> 
> 
> What goes on in the last two calls?
Because your Box::collideWith(Sphere*) has a bug in it. Has nothing to 
do with your double dispatch, which appears to be working perfectly.




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