Swift’s AnyObject
You can also use AnyObject as a constraint on protocols:
protocol MyDelegate: AnyObject. Now the implementers are known to have reference semantics, and withT: MyDelegateyou can have weak references to T, as before. You can even have weak references toany MyDelegate, allowing swapping between delegates of different types.What you might run into, though, is that
any MyDelegateis not itself AnyObject.[…]
Because it carries more information than just a single object reference: it also has a “witness table” pointer, the run-time representation of a protocol conformance.
[…]
But wait, Objective-C never had this problem! The
id <MyDelegate>type doesn’t take up more than a single-object-reference to store! But that’s because ObjC protocols aren’t represented as tables of methods; they’re just promises that the implementing class has methods with particular names.
Previously:
- Equality in Swift: NSObject, Subclasses, and Existentials
- Swift Generics 2: Existentials Boogaloo
- Does Swift Call the Protocol Extension or Subclass Implementation?
- Swift Protocols Wish List
- Swift Protocols
