Re: NSSound Reimplementation

[David Chisnall]

On 16 Jul 2009, at 17:26, Lars Sonchocky-Helldorf wrote:

> Maybe it's not clear to everybody what benefits your patch  
> introduces. So maybe it would be a good idea to give a short  
> enumeration of all the gains to the broader public (I know you're  
> good at writing technical articles since I read quite a few off  
> them :-)).

As I wrote in my first email, it provides the same benefits as Apple's  
non-fragile ABI:

You can add or re-arrange instance variables in a class without  
breaking the ABI.  You can also remove private instance variables.   
Instance variable offsets are now stored in a global variable, rather  
than being hard-coded, and are set when the class is loaded by the  
runtime.  This needs a small amount of compiler and runtime support.   
The runtime support was in the diff I sent to this list, the compiler  
support is in clang (and hopefully someone will add equivalent support  
to GCC).

Unlike the Apple implementation, it does not require the superclass to  
be compiled with the non-fragile ABI, so you can still compile GNUstep  
with the old ABI and then create subclasses of GNUstep classes  
compiled with the non-fragile ABI.  If you rearrange or add ivars in a  
GNUstep class, then the subclass will still work correctly, as long as  
it was compiled with -fnonfragile-abi.

David