On 23 Aug 2008, at 10:13 pm, Michael Ash wrote:
On Sat, Aug 23, 2008 at 7:41 AM, Graham Cox <[EMAIL PROTECTED]>
wrote:
I have a class for which equality can be defined as having the same
internal
string value (which happens to be a UUID-turned-string). I can easily
implement isEqual: based on that but the docs say I also need to
implement
-hash. Any pointers on what is a good way to do that? Could I just
safely
defer to the -hash returned by the string in question?
The implementation of -hash should *always* match the implementation
of -isEqual:.
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. If you compare only one thing
for equality, return it (if it's a primitive) or its hash value (if
you call isEqual: on it).
Thanks guys - works fine.
cheers, Graham
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