On Mar 11, 2004, at 2:33 AM, Maurice Rabb wrote:

> identityHash
> 	^((self class asOop bitShift: 8)
> 		bitXor: (self size bitShift: 4))
> 		bitXor: self asOop

The only problem with this is that it can't be preserved across 
#become:, as #identityHash currently is.  For that reason we may want 
to make this #extendedHash or something, and only use it for 
IdentitySets that we expect to grow very large and where we know that 
#become: isn't being used.