Who is responsible for releasing objects in an array when copying?

cocoa, memory-management, nsarray, objective-c

Solution

I think the previous answers have missed the point, or else the asker was pretty unclear. The actual question isn't talking about either array, but rather the array contents:

who is responsible for releasing the objects contained in the array? Is it main() or array2?

Both `array1` and `array2` are responsible for releasing the objects.

From the NSArray documentation:

"Arrays maintain strong references to their contents—in a managed memory environment, each object receives a retain message before its id is added to the array and a release message when it is removed from the array or when the array is deallocated."

To begin with, each of the objects are retained by the NSArray `array1`. When you create `array2` via `-mutableCopy`, you get an NSMutableArray which points to the same objects, and retains each of them again. If you were to release `array1` at this point, when its `dealloc` method were called it would release each of the objects it contains. However, `array2` has retained them, so the objects won't be destroyed — only when their retain count reaches 0, which would happen if `array2` were destroyed and nobody else has retained any of the objects (or when they are removed from `array2`).

Since collection classes (arrays, sets, dictionaries, etc.) handle retaining and releasing their contents, all you have to worry about is retaining or releasing the collection itself. Since you used `-mutableCopy`, remember that you have implicitly retained `array2`, so you should release it when you're done with it.

Problem

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