Subclassing NSMutableDictionary

Question

I am trying to implement a subclass of NSMutableDictionary that returns nil instead of throwing a NSUndefinedKeyException when the key is not present in the Dictionary.

Answer 1

Here's your problem. NSDictionary (and its mutable counterpart) is part of a class cluster (read more about them here, under the 'Class Cluster' heading), and should not be subclassed because it causes problems such as what you've mentioned (read the subclassing notes in the NSDictionary Class Reference). Whatever it is you need to do, you're going to have a way to extend the classes you want to use in order to do what you want to do. For instance, the above code can easily be placed in a category (read more about categories here).