On Aug 23, 2008, at 12:26 PM, Jeff Johnson wrote:
If you compare primitives in -isEqual:, you should combine them
(using
xor or the like) in -hash. If you compare objects by calling -
isEqual:
on them, you should combine their hashes (using xor or the like). If
you do some of each, combine them all.
What's the motivation for combining hashes in this case? I've
wondered what is the best thing to do when isEqual: is based on
comparing multiple ivars; I typically just use one of them for the
hash.
It's a documented requirement of the isEqual: and hash methods that
the hash must be the same when isEqual: returns YES. Thus, whatever
logic that returns YES in isEqual: must have some kind of match in
hash.
-Jeff
Also, you're probably less likely to have collisions by combining.
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