[Pharo-users] Weakness

[Ben Coman]

I'd like to learn a bit more about the implementation of Weak objects.  
For example, I see...

Magnitude>LookupKey>Associaton >> key: aKey value: anObject
   key := aKey.
   value := anObject

Magnitude>LookupKey>WeakValueAssociaton >> key: aKey value: anObject
   key := aKey.
   self value: anObject
Magnitude>LookupKey>WeakValueAssociaton >> value: anObject
   self at: 1 put: anObject

Magnitude>WeakKeyAssociation >> key: aKey value: anObject
   self basicAt: 1 put: aKey.
   value := anObject

The class definitions don't look any different to normal?   I can see 
that the weak classes are doing an  #at:put:  for their respective weak 
attribute, but lots of non-weak classes also use that.
So what is it that makes   WeakValueAssociaton & WeakKeyAssociation   weak ?

cheers -ben