>From
><http://developer.apple.com/documentation/Cocoa/Reference/Foundation/Protocols/NSObject_Protocol/Reference/NSObject.html#//apple_ref/occ/intfm/NSObject/hash>
"If two objects are equal (as determined by the isEqual: method), they
must have the same hash value. This last point is particularly
important if you define hash in a subclass and intend to put instances
of that subclass into a collection."
On Thu, Aug 20, 2009 at 1:30 PM, Bryan Henry<bryanhe...@mac.com> wrote:
> Why do you say that? I haven't noticed any documented requirement that ties
> the implementation details of -hash and -isEqual together.
>
> - Bryan
>
> Sent from my iPhone
>
> On Aug 20, 2009, at 4:27 PM, Clark Cox <clarkc...@gmail.com> wrote:
>
>> On Thu, Aug 20, 2009 at 12:33 PM, David Duncan<david.dun...@apple.com>
>> wrote:
>>>
>>> On Aug 20, 2009, at 12:00 PM, Seth Willits wrote:
>>>
>>>> Returning 0 is certainly simpler :p
>>>
>>>
>>> It is, but you can generally do better than just returning 0, usually by
>>> just extracting some bits from 'self', ala
>>>
>>> -(NSUInteger)hash
>>> {
>>> uintptr_t hash = (uintptr_t)self;
>>> return (hash >> 4);
>>> }
>>>
>>> This satisfies the condition of hash (two equal objects will have the
>>> same
>>> hash code)
>>
>> No it doesn't. Writing the hash method like that basically prevents
>> you from having an isEqual that does anything other than a pointer
>> comparison.
>>
>> --
>> Clark S. Cox III
>> clarkc...@gmail.com
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>
--
Clark S. Cox III
clarkc...@gmail.com
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