On Aug 23, 2008, at 2:05 PM, Adam R. Maxwell wrote:
If I have
@interface Test : NSObject
{
id ivar1;
id ivar2;
}
@end
@implementation Test
- (BOOL)isEqual:(id)other
{
if ([other isKindOfClass:[self class]] == NO) return NO;
return ([ivar1 isEqual:(Test *)other->ivar1] && [ivar2 isEqual:
(Test *)other->ivar2]);
}
- (unsigned)hash { return [ivar1 hash]; }
@end
I believe it's sufficient to use [ivar1 hash], since the object is
only equal if ivar1 is equal in both objects. I was just curious
to know what you gain by using ([ivar1 hash] ^ [ivar2 hash]); is it
possible to know in general if it reduces collisions? Presumably
that depends on the hash table implementation as well.
--
Adam
Right, it depends on the hash table implementation, which we don't
know. Theoretically, it seems likely to reduce collisions. This could
only be confirmed by real-world performance tests, though.
-Jeff
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