Re: [GDL2] NSAutoreleasePool/EOFault

[Richard Frith-Macdonald]

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On 2005-03-12 20:43:15 +0000 David Ayers <address@hidden> wrote:

> But back to NSAutoreleasePool, it currently uses GSObjCClass which will 
> give 
> it the EOFault class.  If it would have used -class, it would have obtained 
> the object's class.  In this case EOFault is indeed preferable as it 
> intends 
> get the faults implementation of release and invoke it. If this release 
> happens to dealloc the object, the fault will be cleared and dealloc is 
> then 
> called with the original isa.  So I guess we're safe.
>
> I think I'll add some comments in NSAutoreleasePool explaining that 
> GSObjCClass is actually not merely a performance issue but that sending 
> -class would break GDL2.

I'm not too worried about losing the implemenation caching in
NSAutoreleasePool if it helps ... it's not a big optimisation, and using
- -class rather than GSObjCClass() would make the caching pointless (so 
nobody
is going to change it to use -class regasrdless of comments in the code).

However, the issue is a bit of a worry ... implementation caching is a
common optimisation technique, and I was actually a little concerned about
using  GSObjCClass() rather than -class, since doing so gives the object no
chance to return another class, and hence provide the 'correct'
implementation of -release for the particular instance.
That being said, accessing the 'isa' ivar of the class directly (pretty much
what GSObjCClass() does) is also a common optimisation technique, and as in
the NSAutoreleasePool case there is often no point caching a method
implementation if you are then going to have the method dispatch overhead of
calling -class, so I think the two teqhniques are commonly used together and
class implementations should expect that.

Given the lack of clarity about this ... would it be a good idea to produce
guidelines to say that, where caching method implementations, we should use
GSObjCClass() in conjunction with -instanceMethodForSelector:, and that
classes should be written expecting this sort of thing to be done?

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