Swift observer pattern.

observer.swift

import Foundation

protocol Observer {
    var id: String { get }
    func update(_ string: String)
}

extension Observer {
    func update(_ string: String) {
        print("\(type(of: self)) に届いた新しい値は \(string) です。")
    }
}

protocol Subject: class {
    var observers: [Observer] { get set }

    func add(_ observer: Observer)
    func remove(_ observer: Observer)
    func notify(newString: String)
}

extension Subject {
    func add(_ observer: Observer) {
        observers.append(observer)
    }

    func remove(_ observer: Observer) {
        for (index, registerdObserver) in observers.enumerated() {
            if registerdObserver.id == observer.id {
                self.observers.remove(at: index)
            }
        }
    }

    func notify(newString: String){
        print("新しい値 \(newString) を observer に通知します。")
        observers.forEach { observer in
            observer.update(newString)
        }
    }
}

final class SubjectA: Subject {
    var observers: [Observer] = []
}

final class ObserverA: Observer {
    var id = UUID().uuidString
}

final class ObserverB: Observer {
    var id = UUID().uuidString
}

let subjectA = SubjectA()
let observerA = ObserverA()
let observerB = ObserverB()


subjectA.add(observerA)
subjectA.add(observerB)
subjectA.notify(newString: "New!")
subjectA.remove(observerB)
subjectA.notify(newString: "New!!!!!!!!!!!!!!!")