Hands-On Design Patterns with Swift

Implementing the Observable class

We'll implement Observable as a generic class, as it should be able to wrap any kind of object:

class Observable<Type> {    typealias Observer = (Type) -> ()    typealias Token = NSObjectProtocol        private var observers = [(Token, Observer)]()        var value: Type {        didSet {            notify()        }    }        init(_ value: Type) {        self.value = value    }    @discardableResult    func bind(_ observer: @escaping Observer) -> Token {        defer { observer(value) }        let obj = NSObject()        observers.append((obj, observer))        return obj    }    func unbind(_ token: Token) {        observers.removeAll { $0.0.isEqual(token) }    }        private func notify() {        observers.forEach { (_, observer) in            observer(value)        }    }}

We can demonstrate the capabilities of this Observer<Type> object through ...