equality and hashing of objects

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1 total messages Started by Paul Burchard Fri, 30 Oct 1992 07:24

#71

Author: Paul Burchard
Date: Fri, 30 Oct 1992 07:24

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I've created a class which redefines the -isEqual: method.  I'd like to be able  
 
to put such objects into HashTables.  The documentation seems to make this logically impossible.  HashTable says:

	If two keys are equal in the sense of isEqual:, then their hashed 
	values must be equal.

But Object says:

	- (unsigned int)hash
	[...] The integer is guaranteed to always be the same for the same id.

Hmmm....so if my -isEqual: comparison depends only on the contents of objects, not their id's, then the only -hash method allowed is one that returns a constant value!  That's a pretty rough restriction for a hash function...

Can anyone clear up this contradiction? 

--
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Paul Burchard	<burchard@geom.umn.edu>
``I'm still learning how to count backwards from infinity...''
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