Why are UIKit delegates "assign"ed instead of "weak"?

Question

As the title states, why are UIKit delegates (assign) instead of (weak)?

See UIPopovercontroller.h for example:

@property (nonatomic, assign) id <UIPopoverControllerDelegate> delegate;

As far as I can tell this provides no benefits over a weakly retained property but a lot of problems where the delegate needs to manage it's own lifetime as a delegate. It this a backwards compatibility issue?

Thanks

Answer 1

Because most of those properties existed before the iOS SDK supported weak properties. The weak attribute is only supported on iOS 5.0 and later.

I would have to guess that once iOS 4.x and earlier is history, they will all be updated to weak.

Answer 2

UIKit is still built without ARC, therefore none of the UIKit classes can use weak references. Even newer classes like UICollectionView use assign for their delegate properties for this reason.