swift - What's the difference between a protocol extended from AnyObject and a class-only protocol?

Question

Both this declaration

protocol SomeProtocol : AnyObject {
}

and this declaration

protocol SomeProtocol : class {
}

seem to make it so that only classes can conform to this protocol (i.e. that the instances of the protocol are references to objects), and have no other effects.

Is there any difference between them? Should one be preferred over the other? If not, why is there two ways to do the same thing?

I am using the latest released Xcode 6.3.1.

Answer 1

This was answered by an official Swift developer (Slava_Pestov) on the Swift forums. Here is the summary:

• You should use AnyObject (protocol SomeProtocol: AnyObject).

• AnyObject and class are equivalent. There is no difference.

• class will eventually be deprecated.