Apple's documentation says that "Define a capture in a closure as an unowned reference when the closure and the instance it captures will always refer to each other, and will always be deallocated at the same time."
So if I understand this correctly, Apple is saying that, in order to define a capture in a closure as an unowned reference. The closure and the instance it captures have to always deallocate at the same time. But how does a closure deallocate? I know that an instance deallocates when there's no strong references to it. But how and when exactly does a closure deallocate?