Hi Guys,

Finally hacked together an implementation of Ephemerons for Squeak. 
If you wonder what that is:

An Ephemeron is an object which refers strongly to its contents as long as
the
Ephemeron's key is not garbage collected, and weakly from then on.
Ephemerons 
solve a problem which is commonly found when trying to "attach" properties
to 
objects by using a registry. When some property should be attached to an 
object, the property should (in terms of GC behavior) typically have the
life-
time that an instance variable of this object would have. However, this is 
complicated by having an external association between the object and its 
property such as:

registry ------------> association -------------> object
				   |
				   |
				   |
				   v
				property

Here, the registry (a third party) will hold onto the association itself
which 
would require manual removal from the registry (instead of automated garbage

collection). While this problem can be always be solved in any given
concrete 
situation by using one of the various weak association types, choosing 
the 'right' kind of association depends on a variety of factors some of
which 
can change dynamically.

Ephemerons solve this problem by defining that the 'contents' (value) of an 
Ephemeron will be held strongly until the key is known to be garbage 
collected. From then on, the contents of the ephemeron will be held weakly. 
Therefore, the contents of an ephemeron can only become eligible for garbage

collection if and only if the key is garbage collectable which is the exact 
behavior which we would observe for an instance variable of the object.

The package is up at SqueakMap at
	http://map1.squeakfoundation.org/sm/packagebyname/Ephemerons
and will naturally require a new VM before the tests turn green.

Cheers,
  - Andreas