How to add properties to NSMutableArray via category extension?

I know that I can "subclass" an NSMutableArray using "category extensions," i.e. @interface NSMutableArray (MyExtension), to add new functions to the class. However, is there a w开发者_JAVA百科ay using category extensions to also add new properties to the extension?

Note that @interface NSMutableArray (MyStuff) is a category and not a class extension. They are similar in this context, but actually do have quite a few different details.

You can't add storage to an existing class through either mechanism. You can use Associative References to associate data with an instance, though.

As you said, categories can add only methods to a class, not ivars. You could declare property and setProperty: methods in the category, but I'm not sure where you'd store the actual data of your pseudo-property.