Protocol func returning Self

Question

I have a protocol P that returns a copy of the object:

protocol P {
    func copy() -> Self
}

and a class C that implements P:

Answer 1

Following on Rob's suggestion, this could be made more generic with associated types. I've changed the example a bit to demonstrate the benefits of the approach.

protocol Copyable: NSCopying {
    associatedtype Prototype
    init(copy: Prototype)
    init(deepCopy: Prototype)
}
class C : Copyable {
    typealias Prototype = C // <-- requires adding this line to classes
    required init(copy: Prototype) {
        // Perform your copying here.
    }
    required init(deepCopy: Prototype) {
        // Perform your deep copying here.
    }
    @objc func copyWithZone(zone: NSZone) -> AnyObject {
        return Prototype(copy: self)
    }
}