Re: Pluggable widget types and implementations

[Tim Janik <timj imendio com>]

On Fri, 8 Dec 2006, Tristan Van Berkom wrote:

> On Fri, 2006-12-08 at 17:49 +0100, Tim Janik wrote:
> [...]
> > > This abstraction would ensure that there is no confusion at the GType
> > > level, if we start substituting types at the GType level then types
> > > will inevidably be substituted underneath unsuspecting code, that
> > > doesnt sound safe to me at all,
> >
> > we will not do that. never ever. i've adressed that in another
> > email already:
> >    http://mail.gnome.org/archives/gtk-devel-list/2006-November/msg00133.html
> > i.e. we guarantee that:
> >    G_TYPE_FROM_INSTANCE (g_object_new (TYPE_FOO, NULL)) == TYPE_FOO.
> > holds, you may assert that in your code. we will not break that guarantee.
> >
> > let me use your words: we will not substitute types at the GType level.
>
> I see, thank you very much for your patience in describing this,
> for my concerns:
>  a.) G_TYPE_FROM_INSTANCE(g_object_new(TYPE_FOO)/foo_new()) == TYPE_FOO

these are actually two cases, g_object_new and foo_new.
if you read my original proposal again:
  http://mail.gnome.org/archives/gtk-devel-list/2006-November/msg00125.html
you will see that i was suggesting that we change all gtk_*_new() functions
(note, this affects only GTK functions) to return instances *conforming*
to the requested widget types. that's what the pluggable widget types for
Gtk+ is all about. so for the GTK namespace, only these will hold:

  G_TYPE_FROM_INSTANCE (g_object_new (GTK_TYPE_FOO, NULL)) == GTK_TYPE_FOO
  GTK_IS_FOO (gtk_foo_new())

>  b.) IS_FOO (g_factory_create (TYPE_FOO))

this should hold. yes.

so for Gtk+, the idea is to change internals like this:

 GtkFoo*
 gtk_foo_new (void)
 {
-  return g_object_new (GTK_TYPE_FOO, NULL);
+  return g_factory_create (GTK_TYPE_FOO, NULL);
 }


> Knowing that the above assertions hold, completely settles my concern.

hope your concerns are at least 66.6% settled now ;)

> Cheers,
>                   -Tristan

---
ciaoTJ