Stack overflow when defining subscript on CKRecord in Swift

Question

This question asks whether one can use subscripting with CKRecord in Swift. While I already knew how to do what the questioner wanted, every permutation of it g

Answer 1

After some testing and debugging (via a subclass), I discovered that, for CKRecord, objectForKey: does indeed call objectForKeyedSubscript:. Also, implementing subscript in a Swift class that is marked @objc implicitly (by descending from NSObject) or explicitly means that subscript is implemented as objectForKeyedSubscript:.

This means that implementing subscript on CKRecord in an extension hides the default implementation, which causes the stack overflow.