Weak references.

[Jarrett Billingsley]

I've been looking at some of my old nonagon code, and as I'm sure you've all 
experienced looking at your old code, I'm just _cringing_ at some of the 
things I did in it ;)

One thing that I've noticed would be nice to have, however, would be weak 
references to some objects.  For example, I have "brush" objects which 
encapsulate a bunch of visual settings (textures, material, blending modes 
etc.).  These are referenced by objects that can be rendered.  Some of these 
brushes need to be updated often (i.e. every frame to update the environment 
mapping matrices).  So I keep a list (table) of all instances of this brush 
class so I can easily loop through them and update them all.

However when their owners disappear, I end up with uncollectable brushes, 
since they are still being referenced by that table.

So what would be nice to have happen would be to have that table be a table 
of _weak references_ to brush objects.  Then, when no more real references 
existed, they could be collected, and I wouldn't be keeping them around for 
no reason anymore.

I've looked into the scrapple weakref implementation, but it doesn't seem to 
do what I want.  Seemingly it only works if the object that it references is 
explicitly deleted.  I want the weakref to become null if the object that it 
references is collected in any way.

Is this possible at all?  Am I just not using Bill's weakref properly?