Protocol Property Subclassing.

ProtocolPropertySubclassing.swift

import UIKit

class ViewA: UIView {
}

class ViewB: UIView {
}

protocol ViewController: class {
    typealias View: UIView
    var view: View { get }
}

class ViewControllerA: ViewController {
    var view: ViewA {
        get {
            return ViewA()
        }
    }
}

class ViewControllerB: ViewController {
    var view: ViewB {
        get {
            return ViewB()
        }
    }
}

What I originally intended:

import UIKit

class ViewA: UIView {
}

class ViewB: UIView {
}

protocol ViewController: class {
    var view: UIView { get }
}

class ViewControllerA: ViewController {
    var view: ViewA {
        get {
            return ViewA()
        }
    }
}

class ViewControllerB: ViewController {
    var view: ViewB {
        get {
            return ViewB()
        }
    }
}

Last edit based on: https://twitter.com/uint_min/status/598729211730235392