Re: person interested in GNUstep development

[David Chisnall]

On 22 Feb 2013, at 10:56, Maxthon Chan <address@hidden> wrote:

> Dear Johan:
> 
> Hello.
> 
> 1) Objective-C 2.0 is creation of Apple Inc. and is incorporated into OS X 
> 10.5 (partially) / 10.7 (completely) and iOS 4.3 (partially) / 5.0 
> (completely). For GNUstep, the latest svn build of GNUstep can support most 
> of the Objective-C 2.0 features if using clang as the compiler.

Objective-C 2 does not define a language, it is a brand.  It meant NeXT-style 
Objective-C with the new exception syntax, fast enumeration, and declared 
properties.  Newer versions of Objective-C do not have version numbers 
(possibly because we mocked Apple for releasing Objective-C 2 as the release 
after Objective-C 4, which was the last version number that NeXT gave to the 
language).

Newer (post-Objective-C-2) features are:

- Interoperable exceptions (C++ throw and catch works with Objective-C types, 
an Objective-C object thrown with throw can be caught with @catch).
- Blocks (not just Objective-C, but heavily used in Objective-C, and with 
runtime support for using blocks as methods)
- Garbage collection (introduced and then deprecated, as the semantics were 
very poorly thought out)
- Lots of new runtime features (e.g. associated objects)
- Automatic reference counting
- Braindead syntax for number literals and collections.  

All of these are supported by the combination of clang and the GNUstep 
Objective-C runtime.  We also support a few features beyond those in Apple's 
implementation:

- Typesafe dispatch.  Selectors with mismatched types will cause stack 
corruption on Apple's runtime, raise an exception on ours.
- Prototype-based orientation.  You can add methods to individual objects.

> Due to historical reasons that is related to versions and changes of GPL 
> license and Apple Inc, GCC never get full Objective-C 2.0 support. Apple is 
> now participating in another compiler project, clang, which is now the 
> leading compiler for Objective-C and implemented full Objective-C features.

There were various reasons for Apple discontinuing GCC support.  The GPL was 
one, but the poor layering in GCC was another - it's very hard technically to 
reuse GCC front ends for things like syntax highlighting, refactoring tools, 
and so on, even if the license is not a problem.

David