Well in this case I subclassed them so I could have the backing data source only weakly reference the items in the dictionary/array and because I subclassed them I can use them wherever NSDictionary or NSArray is an accepted parameter.

Apple's documentation also gives some examples:

https://developer.apple.com/library/ios/#documentation/Cocoa...

https://developer.apple.com/library/ios/#documentation/Cocoa...