Re: Implementing isEqual: and hash
Re: Implementing isEqual: and hash
- Subject: Re: Implementing isEqual: and hash
- From: Jeff Johnson <email@hidden>
- Date: Sat, 23 Aug 2008 12:32:16 -0500
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.
_______________________________________________
Cocoa-dev mailing list (email@hidden)
Please do not post admin requests or moderator comments to the list.
Contact the moderators at cocoa-dev-admins(at)lists.apple.com
Help/Unsubscribe/Update your Subscription:
This email sent to email@hidden