Re: Generics vs. Message passing: object namespaces

On 2/23/07, Jeremy H. Brown <[email protected]> wrote:
>
> "Matt Knox" <[email protected]> writes:
> > If I understand it correctly, your point is that if you need  the draw
> > method from gun, picture, blood, and duel modules, that in an
> > object-dispatch system, you can say:
> >
> > gun.draw args
> > duel.draw args
> > ...etc.
> >
> > instead of
> > (draw_gun gun args)
> >
> > But it seems that it should be trivial to have, in a CLOS-style generic
> > function system, 'draw' bound to a function that would look at the type
> of
> > its first argument and dispatch to the appropriate GF. Then you'd have:
> >
> > (draw gun args)
> > ...
> > and the only differences would be syntax and the ease with which
> > autocompletion could be done.
> >
> > Am I missing something?
>
> Multiple inheritance.  I could have a gun-widget class which inherits
> from both gun and picture.  In your scheme, when I say (draw widget
> args), which version of draw should execute?  If there's any risk of
> this sort of subclassing, you want to write (picture:draw widget args)
> or (gun:draw widget args) explicitly.
>
> (Fans of the model-view-controller design pattern will look down on
> this specific use of MI, of course.)
>
> Jeremy
>

If your OO system has a full linearization, (like Dylan and unlike CLOS, I
think), then you have an unambiguous criterion, wouldn't you?


-- 
(def (eval e l d c)
  (if  (atom? e)
      ((ahandler (type e)) e l d c)
      (eval (car e) l d
              (fun (x)
                 (evapp x (cdr e) l d c)))))