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

[David Chisnall]

On 21 May 2009, at 10:34, Wolfgang Lux wrote:

> Have you ever looked at what Apple is doing? I can use executables  
> compiled on Mac OS X 10.2 on Mac OS X 10.5 without any problems and  
> Mac OS X does ship with only a single instance of all its libraries/ 
> frameworks

Only half of this is true.  Apple only ships one version of its  
frameworks.  Each framework, however, contains different versions of  
the libraries.  You may have noticed all of the OS X version macros in  
the headers.  Each of those defines the parts of the interface that  
are visible in a particular version of the framework, but they are  
also used when compiling.  Each version of OS X has a  
Foundation.framework containing several libFoundation.dylib files, one  
compiled for compatibility with each previous version.  Without access  
to their source, I can't be completely sure how they are doing this,  
but my guess is that each ivar and each method - even each typedef -  
has the same feature macros in front of it and their build system  
automatically generates a backwards-compatible version as long as  
these changes are made.

It would be nice if GNUstep make had facilities for doing this, but I  
imagine it would be a lot of effort.  It would also be easier if we  
could rely on a loader that supported frameworks properly, but I  
believe Matt Rice is the only person who has one of these on a non- 
NeXT/Apple platform.

David