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?

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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.

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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.