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objective-ccopyretainretaincount

Effect on object before and after retain & copy

I have two questions:

  1. I have an object, call it X. When I assign retain to object X ([x retain]) and then change data in the object X, what will be the retain count of X?

  2. I have two objects, A & B. I first do a copy like this:

    B = [A copy];

and now I change data in object A. Will the B data also change, and what will be reference count of both A & B before and after the change of data?

Solution

  • For 1, if you mean change the data like x.foo = y, the retain count doesn't change. If you mean x = y, then the retain count of x changes to whatever the retain count of y is, because x is y.

    For 2,

    The data of B is unchanged. The retain count of B is 1. The retain count of A is the same as before the copy.

    That's the normal case, but I think an object can choose to return a non-new object from copy. I think non-mutable NSStrings will return themselves as the copy, so the retain count of B might not be 1, and the retain count of A will be increased by 1. Basically, you can't rely on it.