On Thu, Aug 20, 2009 at 1:47 PM, Shawn Erickson<[email protected]> wrote: > On Thu, Aug 20, 2009 at 1:37 PM, Kyle Sluder<[email protected]> wrote: > >> P: Two objects are equal. >> Q: They have the same hash. >> >> P -> Q. >> >> Note that Q does not imply P. > > Or said another way... > > If the hash of ObjectA is equal to the hash of ObjectB then ObjectA > _could_ be equal to ObjectB. If their hash differ they cannot be > equal. The use of a hash to do a quick reject of equality is common > for stl collections, java collections, Cocoa collections, etc.
Yes, and two different objects will have different pointer values. If the hash is based on the pointer values, then two different objects cannot have the same hash, regardless of whether or not they are equal. Hence, that implementation of hash is broken for any object that does anything other than a pointer comparison in -isEqual:. -- Clark S. Cox III [email protected] _______________________________________________ Cocoa-dev mailing list ([email protected]) 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: http://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to [email protected]
