Lightweight property observer in swift

Notifiable.swift

final class Notifiable<T> {
    
    typealias CompletionHandler = ((T) -> ())
    
    private var propertyChanged: CompletionHandler? = nil
    
    var value: T {
        didSet {
            guard let observer = propertyChanged else { return }
            observer(value)
        }
    }
    
    init(value: T) {
        self.value = value
    }
    
    func observe(_ completion: @escaping CompletionHandler) {
        propertyChanged = completion
    }
    
    deinit {
        propertyChanged = nil
    }
}

// In action
let someValue = Notifiable<String>(value: "Hello World")

someValue.observe { value in
    print("value is changed = \(value)")
}

someValue.value = "Hello Farooq"