[Pyobjc-dev] weakref-like behavior on ObjC subclasses

[James R E. <ea...@ba...>]

I have a class that implements an observer pattern in python.   
Observables maintain weakrefs to listeners that have been registered  
with them such that, when a listener goes out of scope, the observable  
doesn't keep it alive.  Of course, this mechanism fails as soon as a  
listener inherits from an ObjC class because weakref doesn't support  
ObjC classes.

At this point, my workaround is to store a strong reference if the  
listener can't be weakref'd.  I'm not happy about this solution  
because it now creates different behaviors depending on whether the  
object can be weakref'd.  If it can, then the listener is  
automatically unregistered from the observable when its lifespan is  
up.  If it can't, however, then the object must be manually  
unregistered before deletion will ever occur.

This is where the problem arises in PyObjC.  Is there any mechanism  
through which I can approximate a weak reference to an ObjC object in  
Python?

I tried doing some magic by checking the retainCount() of my objects,  
but that seems to always be the same, no matter how many Python  
objects hold a ref to the ObjC instance.

Thanks in advance!
James

PS: I'd love to be able to use an NSHashTable with  
NSHashTableZeroingWeakMemory, but I need to maintain 10.4 support on  
this project. :-(

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