Re: Relationship between -isEqual and -hash
Re: Relationship between -isEqual and -hash
- Subject: Re: Relationship between -isEqual and -hash
- From: Dustin Voss <email@hidden>
- Date: Sun, 21 Jan 2007 22:27:18 -0800
On 19 Jan 2007, at 1:46 PM, Jeffrey J. Early wrote:
Quick question:
It is well stated in the documentation that the following must be
true:
If two objects are equal (as determined by the isEqual: method),
they must have the same hash value.
My question is whether the reverse must also hold?
I assume because it's not mentioned in the documentation (and I
can't think of a reason why), it must be okay.... but that isn't
necessarily good reasoning :-)
In my code I have a dictionary that I want to behave in a
particular way. I'm using objects as keys where if two objects are
'close enough', they will return the same value from the
dictionary, even if these objects aren't equal in the -isEqual:
sense. So when objects are 'close enough', I have them return the
same hash value.
It's all laid out here: http://cocoadev.com/index.pl?HashingAndEquality
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