Re: ABI Compatibility (was Re: Installation woes for the average user...)

[Richard Frith-Macdonald]

On 20 May 2009, at 23:17, Yavor Doganov wrote:

> Richard Frith-Macdonald wrote:
> > On 20 May 2009, at 20:54, Yavor Doganov wrote:
> > > If I understand correctly, you say that between 1.13 and 1.19 (for
> > > example) not all soname bumps were warranted.
> >
> > No that's absolutely *not* what I said.
> >
> > I pointed out that the large majority of the recent base library
> > releases (including the latest one) did *not* change the soname!
>
> I feel we are miscommunicating.  Let me try to clear this out -- I am
> counting only the major releases when there was a soname bump; the
> regular point releases are not interesting for this discussion.

Then the discussion seems rather pointless ... since what you are  
calling the 'major' releases are those were we make ABI changes and  
bump the soname.

> 1.13.0 was released on 2006-08-28 according to the ChangeLog entry, so
> for less than 3 years you put your word that you broke the ABI 6
> times?  That's astonishing given the fact that Base is advertised as a
> fairly stable library (and *it is*, more or less).

Yes, there's a *lot* of functionality there, and the core part of it  
is very stable, so the chances are that any individual ABI change will  
not break your application because the app will not be using the  
feature concerned.  In particular, changes to class instance variable  
layouts will only effect applications which subclass the class  
concerned ... and that's very, very few applications for most classes.

Chasing MacOS-X is a problem for us .. sometimes Apple make changes  
which require ABI changes.  Often they add new stuff, which we try to  
add too.  If we don't get the additions quite right in one release, we  
need to fix them in the next release, and that fix may change the ABI  
with respect to the new feature, even though the ABI of the main part  
of the library is stable/unaffected.  This can be something as trivial  
as implementing an obscure method with an argument of the wrong type  
(eg a long rather than an int), then having to change the argument  
type in a later release to match MacOS-X.
Given that, I think it's more likely that we sometimes make a mistake  
and release without bumping the soname when we technically should,  
than that we accidentally bump the soname when we don't need to.