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How do you properly override isEqual: in Objective-C? The "catch" seems to be that if two objects are equal (as determined by the isEqual: method), they must have the same hash value. The Introspection section of the Cocoa Fundamentals Guide does have an example on how to override isEqual: , copied as follows, for a class named MyWidget : - (BOOL)isEqual:(id)other { if (other == self) return YES; if (!other || ![other isKindOfClass:[self class]]) return NO; return [self isEqualToWidget:other]; } - (BOOL)isEqualToWidget:(MyWidget *)aWidget { if (self == aWidget) return YES; if (![(id)[self name] isEqual:[aWidget name]]) return NO; if (![[self data] isEqualToData:[aWidget data]]) return NO; return YES; } It checks pointer equality, then class equality, and finally compares the objects using isEqualToWidget: , which only checks the name and data properties. What the example doesn't show is how to override hash . Let's assume there are other properties that do not affect equality, say age . Shouldn't the hash method be overridden such that only name and data affect the hash? And if so, how would you do that? Just add the hashes of name and data ? For example: - (NSUInteger)hash { NSUInteger hash = 0; hash += [[self name] hash]; hash += [[self data] hash]; return hash; } Is that sufficient? Is there a better technique? What if you h

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