El 07/08/2006, a las 22:09, Dietmar Planitzer escribió:
There are a ton of highly interesting things there. I like all of
them - but my personal favorit is the AGC stuff.
Could you comment a bit more about that? What are some of the
highly interesting things in there. I've looked at the CVS
repository but I don't know enough to really interpret what's in
there that's going to benefit me; from my perspective as an
Objective-C user (not a compiler hacker).
Jason has already listed some of those features (method attributes,
agc, properties). Now a disclaimer, before we go further:
Everything that I say below is only and exclusively gathered from the
GPL sources in the public gcc repository, publicly available Apple
documentation and publicly available Apple source code. The gcc
sources have been accessible to the public for at least 3/4 of a year
now (that's when I first stumbled over them). However, whether those
sources represent the gcc specific bits of ObjC 2.0 or not is
something that must be left to the realm of speculation as the
sources nowhere mention that name. Further, the greater goal of some
of the changes that can be found in the sources can not be
satisfactorily explained without access to the missing pieces of the
puzzle, namely the corresponding ObjC runtime and Foundation
framework. Since those components are not publicly accessible, we can
only speculate about the purpose of those changes.
Now what can be seen there ?
A complete new ABI that seems to organize the runtime data structures
in a more efficient way. There is more that could be said about this,
but as mentioned above, figuring out what the exact purpose of each
and every of the many changes is without access to the corresponding
runtime is wild guessing in the dark.
Support for automatic garbage collection. The gcc man page that comes
with Xcode 2.2+ has a description of how this feature can be enabled
and how it basically works. The GC uses write barriers for it's
implementation and seems to support a generational collection
algorithm (see /usr/include/objc/objc-auto.h on a Tiger system with
Xcode 2.2+ installed). Looking at the sources of the current Tiger
ObjC runtime (objc-274, available from Apple's open source page) it
seems that the AGC can be enabled/disabled on a per-application
basis. I.e. application A can run with the AGC, application B can run
with reference counting instead. By the way, the AGC has been
shipping with every copy of Tiger for a year now. Look into /usr/lib/
libauto.dylib.
A faster message dispatching mechanism. How it works, I've forgotten
by now :)
As Jason already mentioned: properties aka auto-generated getters/
setters. Looks like that you are able to specify the behavior of the
getter/setter. I.e. should it reference a passed in object or should
it copy it.
Another thing is a thing to iterate over those things called
collections aka foreach().
There are probably other things that I've overlooked or forgotten.
But those things would in my opinion already make ObjC a much more
powerful language than what we have today. Assuming that they find
their way into a shipping version of Mac OS X.
Regards,
Dietmar Planitzer
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