Re: changing inheritance == API breakage

[Tim Janik <timj gtk org>]

On Sat, 7 Jan 2006, muppet wrote:

> [/me takes a few more swats at the horse, in case it's still breathing...]
>
> Tim mentioned something the other day about glib's type system being 
> completely dynamic, and that code must be prepared for the insertion of new 
> types.  This didn't sit well with me, but i couldn't express it, and got 
> sidetracked.
>
> It occurred to me on the plane this evening that the hierarchy actually 
> cannot be dynamic, because it is encoded in structure definitions.  By using 
> same-size structures and casting you can avoid most problems, but changing 
> the hierarchy of a GObject derivative does, indeed, result in API breakage.
>
> Consider this code:
>
>      if (widget->object.parent_instance.ref_count > 1) {
>          ...
>      }

accessing a widget's parent type other than through explicit casts
is not supported for many years. we don't even have a consistently used
naming convention for the embedded parent class type in a structure.

> --
> I think it worked on the Wiley Coyote model of project management - if
> at any point you looked down and realised what you were doing was
> impossible then you'd instantly fail.
>  -- Simon Wistow

---
ciaoTJ