Rule Definition
If -isEqual: determines that two objects are equal, they must have the same hash value. This is why, if you override the isEqual method, you also need to override the hash method.
Reference
https://developer.apple.com/library/ios/documentation/General/Conceptual/DevPedia-CocoaCore/ObjectComparison.html
Related Technologies
Technical Criterion
Complexity - OO Inheritance and Polymorphism
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