Re: BUG #1589: The whole concept of forces/move_with_forces/forces_holder needs to be rethought

[Gervase Lam]

> Subject: Re: BUG #1589: The whole concept of
> forces/move_with_forces/forces_holder needs to be rethought
> From: Ingo Ruhnke <address@hidden>
> Date: 04 Nov 2002 23:21:08 +0100

> class Pingu
> {
> public:
>   template<class T>
>   void check_collision(const T& col)
>   {
>     if (col(6, 5))
>       std::cout << "Something collided" << std::endl;
>     else
>       std::cout << "Nothing collided" << std::endl;
>   }
> };
>
> struct Coll
> {
>   bool operator() (int a, int b) const {
>     return a > b;
>   }
> };
>
> int main()
> {
>   Pingu a;
>   a.check_collision(Coll());
> }

Sorry if this is a naive question.  Why do member templates have to be 
used?  Couldn't something like the following do?

/** First, the base class **/
class PinguAction
{
public:
  virtual void move_to();
  virtual bool check_collision(int a, int b);
}

bool PinguAction::move_to()
{
// blah blah
  if (check_collision(a, b))
// blah blah
}

bool PinguAction::check_collision(int a, int b)
{
// "Default" collision function
}

/** An action that has specialised collision checking **/
class PinguAction::AnAction
{
public:
  virtual bool check_collision(int a, int b);
}

bool PinguAction::check_collision(int a, int b)
{
// "Overrides" base collision function
}

That's the basics of it.  OK, a few small things could be improved here.  
But why not use this basic idea rather than member templates?

Thanks,
Gervase.