Swift — Require classes implementing protocol to be subclasses of a certain class

Question

I\'m creating several NSView classes, all of which support a special operation, which we\'ll call transmogrify. At first glance, this seems like t

Answer 1

For Swift 4, based on @Antoine's keen insight:

Create a protocol then use a typealias to give a cleaner name to a type that conforms to both a class and the protocol.

protocol Transmogrifiable {
    func transmogrify()
}
typealias TransmogrifiableView = NSView & Transmogrifiable

You can then define a class that inherits from that type....

class ATransmogView: TransmogrifiableView {
    func transmogrify() {
        print("I'm transmogging")
    }
}

....or define a class that inherits from the protocol and a subclass

// this also qualifies as a TransmogrifiableView

class BTransmogView: NSTextView, Transmogrifiable {
    func transmogrify() {
        print("I'm transmogging too")
    }
}

Now you can do this.

func getTransmogrifiableView() -> TransmogrifiableView {
    return someBool ? ATransmogView() : BTransmogView()
}

And this now compiles.

let myView: TransmogrifiableView = getTransmogrifiableView()
let theSuperView = myView.superView