title: Implementing a mutable IndentityDictionary in Objective-C?
body: <p>Trying out some older code and I've come across an IdentityDictionary. From what I know NSDictionary uses equality, not identity to compare Objects. Judging by it's use it seems I would need a mutable IdentityDictionary anyway?</p>
  
  <p>I've read two threads on this and it seems to be quite difficult to do, Class clusters, hash functions and so on. </p>
  
  <p><a href="https://stackoverflow.com/questions/12403561/does-nsdictionarys-objectforkey-rely-on-identity-or-equality">Does NSDictionary's objectForKey: rely on identity or equality</a></p>
  
  <p><a href="https://stackoverflow.com/questions/1112373/implementing-hash-isequal-isequalto-for-objective-c-collections">Implementing -hash / -isEqual: / -isEqualTo</a></p>
  
  <p>How would one go about doing this?</p>