Re: Generics vs. Message passing: object namespaces

On 2/23/07, Michael Walter <[email protected]> wrote:
>
> On 2/23/07, Matt Knox <[email protected]> wrote:
> > On 2/23/07, Michael Walter <[email protected]> wrote:
> > > On 2/23/07, [email protected] <[email protected]> wrote:
> > > > > 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?
> > > >
> > > >
> > > >     No, I think that is correct, but that is not how CLOS-style
> generic
> > > > OOP works, the original subject of criticism. [...]
> > >
> > > In what way is using dynamic dispatch not how CLOS-style generic OOP
> > > works? I mean, this seems to be pretty much what defgeneric/defmethod
> > > are for.
> > >
> > > Regards,
> > > Michael
> > >
> >
> > The difference is that if you define 3 different GFs (not different
> methods
> > on a single gf, but 3 different functions) in different source files,
> each
> > with the same name, CLOS does not automatically smash them together into
> a
> > sngle, more generic function.
>
> But why don't you define 3 different methods of the same generic function?
>
> Regards,
> Michael
>

Because you might not have written all three modules.

It shouldn't be hard to make the package system create a dispatch function
when it detected function name collisions.  Then, as long as the argument
types encode enough information to decide which method to call, you're
fine.

-- 
(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)))))