how to add member variable and methods to in built class without subclassing it
cocoa, objective-c
Solution
For methods: you can use categories to add member methods without subclassing. It is a pretty common practice in Cocoa, to add per-framework extensions methods.
For instance variables: starting with Snow Leopard (Mac OS X 10.6), you can use associative references. You use them to simulate the addition of object instance variables to an existing class.
The Objective-C Programming Language is pretty comprehensive on what you can do with both associative references and categories.
Problem
How can I add member variables and methods to an in built class(say, NSString) without subclassing it.