Re: Cocoa Compatible, is it actually possible?

[David Chisnall]

Hi Lucas,


On 26 Jul 2009, at 22:32, Lucas Samaruga wrote:

> Hi all
>
> > From total ignorance.
> Is it possible to make an application fully compatible between Cocoa
> and GNUstep?

Yes, it's possible (at a source level, anyway.  I believe the bundle  
layouts are such that it's also possible to create a .app bundle with  
an OS X binary as well as GNUstep/Linux/BSD/Whatever binaries, but  
I've never actually tried).

In general, if you stick to Foundation and AppKit, your app should  
Just Work™ with GNUstep.  There are a few other frameworks, for  
example the Address Book and CoreData which have GNUstep versions too.

In practice, you will find that the probability of any given class or  
method being supported increases with the age of the API.  Anything  
from OpenStep is pretty-much guaranteed to work with GNUstep.  Most  
things from OS X 10.3 and earlier work.  Quite a few things from 10.5  
work.

Of course, patches for any missing methods are very welcome.  Often  
implementing a missing method (or class) in GNUstep is less effort  
than modifying your application to avoid using it...

> Is there any list of incompatibilities or api differences?

There used to be an automatically-generated list somewhere, but it  
wasn't very accurate.  I'm not sure if it still exists.  If you  
develop with GNUstep and then port to OS X, things are much more  
likely to work than the other way around, as long as you don't #import  
any of the GNUstep extension headers (and, even then, they are often  
available as categories on OS X).

To give you a rough idea of the completeness of GNUstep, I use the  
Apple API documentation when I am writing GNUstep code, rather than  
the GNUstep docs, and haven't come across a missing method that I  
actually wanted to use for quite a while.

David