>If saving memory isn't a priority, there is always the Self way of
>hashing. Dedicate some 12 to 16 bits in the header of each object
>and fill it in from some counter or random number generator when
>the object is created and never change it after that.
>
>Of course, given Squeak's compact headers I don't think this is
>the way to go here.


You don't have to do it that way. You have only 2 bits for a hash. They 
start off in state "no hash". As soon as you take the (larger hash) of 
the object you put the hash in a look aside table and mark the object as 
"hash taken". As soon as the grabage collector gets room (moves the 
object, or deallocates the object behind it) the has is moved to the end 
of the object and make the tags "hash attached".

Alas this wont keep the invariant that objects that compare equal hash 
equal if the object hash depends on the contents and the object is 
modified after the hash is first taken.


Pat Caudill