Re: [Notion-devel] Object inheritance

[Arnout E. <no...@bz...>]

On Tue, Apr 12, 2011 at 09:28:51AM -0400, Etan Reisner wrote:
> I think renaming to "super" is a pointless idea. Either you know what type
> the parent is, in which case typing its name instead of super isn't a big
> deal; or you don't, in which case you can't use super anyway since you
> can't know what to cast it to.

Indeed it is not useful when writing code, but imho it is useful when reading 
code.

> It also doesn't tell you anything useful, since the immediate super
> relationship isn't particularly helpful whereas the type of the member
> actually is (especially if you are simply passing it to another function
> which expects a certain type).
> 
> Consider:
>     WScreen *scr=current_screen();
>     mplex_switch_next(&(scr->mplex));
> versus
>     WScreen *scr=current_screen();
>     mplex_switch_next(&(scr->super));
> 
> Which one tells you immediately that you've gotten the argument type to
> mplex_switch_next right and which one leaves you having to remember and or
> guess?

In this case, when reading this code, I actually do think the second variation
is more readable: you know the code compiles, you can easily guess 
'mplex_switch_next' will take an mplex argument, and the 'super' tells you 
you're calling 'mplex_switch_next' on the screen itself instead of on some 
mplex property of the screen.

> Also consider your given example. In what way is
> > 'rw->scr.super.super.win=None;'
> superior to
> > 'rw->scr.mplex.win.win=None;'
> ?
> 
> The super version reads less well (to me), gives me less information, and
> at that point I would really want a cast (or cast macro) or something to
> hide it (you probably want that in either case really).

Again, while I agree '.super.super' does not look very elegant, you *can* see
at a glance that 'win' is a property of the screen itself (via superclasses)
rather than a property of a property of a property of the screen. The types of
the superclasses in the second variation add confusion rather than information 
imho. 

I think I would prefer 'normal' casts over glib-style macro-casts, but both
of these throw the static typechecking out of the window, which the use of
members (named 'super' or otherwise) avoids.


Kind regards,

Arnout