Re: property API vs fields

[Owen Taylor <otaylor redhat com>]

On Thu, 2006-08-17 at 11:25 +0200, Murray Cumming wrote:
> > On Sun, 6 Aug 2006, Steph Fox wrote:
> >
> >> Hi GTK people,
> >>
> >> The PHP-GTK doc team have hit a point of confusion over the property API
> >> in
> >> GTK 2, mostly because publicly accessible fields hanging over from GTK 1
> >> are
> >> still publicly accessible. We don't know whether to promote the use of
> >> *_get_|set_property() or not, and to some extent that depends on whether
> >> it
> >> will eventually be enforced by the GTK+ team.
> 
> I mean to reply to this earlier.
> 
> GTK+ is very unlikely to change those struct fields, even if they could do
> so while keeping the struct size the same. It would just be too risky
> because someone's hack probably depends on the non-public API. The
> situation is avoided with new code by using the GObject "private" data.
> 
> Do use the property API wherever it exists. It does more than just
> setting/getting a struct field.
> 
> However, some of those struct fields really are public. I forget exactly
> what the rule is, and I can't find the email where this was stated. It's
> either
> - They are public unless marked private.
> or
> - They are private unless marked public.
> 
> Whatever the rule is, it's probably not followed perfectly. A list of
> structs where this isn't clear would probably help people to improve the
> documentation.

The rule is:

 Object instance structures: private unless marked public. (public
   fields are read-only)
 Normal structures: public unless marked private.

However, there are supposed to be *no* places in the GTK+ API where
you have to read an object instance structure field, even if it
is marked public; the intention there is 100% coverage with getters.

Regards,
                                       Owen