import UIKit

class Singleton

{

    static let shared: Singleton = {

        var instance = Singleton()

        instance.name = "default name"

        return instance

    }()

    var name: String = String()

}

class SingletonSubclass: Singleton {

    static var sharedSub: SingletonSubclass = {

        var instance = SingletonSubclass()

        instance.name = "default name"

        return instance

    }()

    var title: String = String()

}

Singleton.shared.name          // ""

SingletonSubclass.shared.name  // ""

SingletonSubclass.shared.name = "haha"

SingletonSubclass.sharedSub.title = "hello"

Singleton.shared.name             // ""

//Singleton.shared.title          // (error)

SingletonSubclass.shared.name     // "haha"

SingletonSubclass.sharedSub.title // "hello"

import UIKit

class Singleton

{

    class func sharedInstance() -> Singleton {

        struct inner { static let instance = Singleton() }

        inner.instance

        return inner.instance

    }

    var name: String = String()

}

class SingletonSubclass: Singleton

{

    override class func sharedInstance() -> SingletonSubclass {

        struct inner { static let instance = SingletonSubclass() }

        return inner.instance

    }

    var title: String = String()

}

Singleton.sharedInstance().name          // ""

SingletonSubclass.sharedInstance().name  // ""

SingletonSubclass.sharedInstance().name = "haha"

SingletonSubclass.sharedInstance().title = "hello"

Singleton.sharedInstance().name          // ""

//Singleton.sharedInstance().title       // (error)

SingletonSubclass.sharedInstance().name  // "haha"

SingletonSubclass.sharedInstance().title // "hello"