Boxing in Swift 4.2

MVVM with Boxing in Swift 4.2

class Box<T>{
    
    typealias Listener = (T) -> Void
    var listener: Listener?
    
    var value: T {
        didSet{
            listener?(value)
        }
    }
    
    init(_ value: T) {
        self.value = value
    }
    
    
    func bind(listener: Listener?){
        self.listener = listener
        listener?(value)
    }
}

//Example for Use
let boxInt: Box<String> = Box("")
boxInt.value = "Bob"

boxInt.bind {
    print("value chanage \($0)")
}

boxInt.value = "John"