SingletonDelegate.swift

protocol SingletonDelegate : class {
    
    func reportSingletonUpdate(value:Int)
}

class Singleton {
    
    private static var privateShared : Singleton?
    
    weak var delegate : SingletonDelegate?
    
    class func shared() -> Singleton {
        guard let uwShared = privateShared else {
            privateShared = Singleton()
            return privateShared!
        }
        return uwShared
    }
    
    class func destroy() {
        privateShared = nil
    }
    
    func somethingHappened() {
        
        guard let del = delegate else {
            return
        }
        
        del.reportSingletonUpdate(0)
    }
    
    private init() {
    }
}

class VC : UIViewController, SingletonDelegate {
    
    override func viewDidAppear(animated: Bool) {
        Singleton.shared().delegate = self
    }
    
    func reportSingletonUpdate(value: Int) {
        print(value)
    }
}