Hi,

> >  So, I propose to define Collection>>hash something like:
> >----------
> >hash
> >	| hash index |
> >	hash _ self species hash.
> >	index _ 0.
> >	self do: [:item |
> >		(index _ index + 1) > 3 ifTrue: [^hash].
> >		hash _ hash bitXor: (((hash bitShift: -6) bitOr: ((hash bitAnd: 16r3F) 
> >bitShift: 6)) + item hash).
> >	].
> >	^hash.
> >----------
> >
> >  How do you think?
> 
> This looks like it corresponds to the implementation of Collection>>= 
> nicely, and should work for any kind of Collection.

  But I was wrong: the order of elements returned by
aSet>>do: varies even the two Sets have "same" elements.
So, sorting the elements with respect to the hash value
before picking the items is needed.

-----------------
hash
	| hash array |
	hash _ self species hash.
	array _ (self collect: [:elem| elem hash]) asSortedCollection.
	array size = 0 ifTrue: [^hash].
	hash _ (hash + (array at: 1)) bitXor: ((array at: array size)).
	^hash.
-----------------

  It would be nice if the instances of Set and Dictionary
hold cached hash value in order to avoid the recalculation
of hash, but it requires VM modification.

  -- Yoshiki