Re: Objective-C 2.0

[David Chisnall]

On 2 Sep 2009, at 12:17, Michael Thaler wrote:

> Hi,
>
> I am currently learning Objective-C on the Mac (using that book:-))  
> and I was
> wondering if Objective-C 2.0 is available on Linux and if it can be  
> used for
> gnustep development.

Yes, it is mostly available, but only if you compile with clang and  
link against Étoilé's ObjectiveC2 framework[1].

> If it is available is it ok to use it for gnustep?

Not for core GNUstep code, but certainly for your own code that you  
want to use on top of GNUstep.

> If it is not available, are
> there any plans to support it?

Yes.

> I think especially having a garbage collector
> would be quite interesting. Personally I think having a GC would be a
> sustantial advantage of gnustep over, e.g. Qt.

GNUstep has supported the Boehm GC for a while.  Gregory has been  
working on porting AutoZone too.  Using GC is generally not a good  
idea, because you will almost certainly find a framework that you want  
to use which doesn't support it (and you will also find you can't port  
your code to the iPhone).  The combination of autorelease pools and  
reference counting is usually enough.

> If it is partly available, which features can (should) be used?

For maximum portability, none.  The features which will work with  
clang and ObjectiveC2.framework are:

- Fast enumeration (support may be missing in some GNUstep classes for  
this; patches welcome)
- Declared properties.
- Zero-cost exceptions (requires all code to be compiled with DWARF  
exception support).
- The new runtime APIs.

Non-fragile ivars are currently working with clang, but only with the  
version of the GNU runtime on my hard disk.  This situation should  
also be fixed shortly.

I've no idea whether the Boehm GC works with clang-compiled code.   
Clang has hooks for supporting GC in the runtime-specific code, which  
are currently unimplemented for the GNU runtime.  These will be added  
when Gregory has finished porting AutoZone.

> Are blocks
> available (which seem to be a propertery Apple extension to C-like  
> languages)?

Yes, with the same requirements (compile with clang, link against  
ObjectiveC2.framework).  Blocks require you to compile your code with - 
fblocks.  You can test for their availability using the __has_feature 
() pseudo-macro.

> Is it possible to write applications that can be compiled on both  
> the Mac
> using Cocoa and Linux using gnustep?

Yes, there are a great many examples of this.  Remember that Objective- 
C 2 is a relatively small set of extensions and Objective-C 1 was used  
to write some very large applications and frameworks for two decades.

David