Simple reactive MVVM with KVO

Mvvmkvo.swift

import UIKit

//
// ViewModel, all KVO compliant to ViewController can observe changes in a decouple way.
//
class MyViewModel: NSObject {
    @objc dynamic var firstName:String = ""
    @objc dynamic var lastName: String = ""
    
    // Fullname, concatenation of first and last.
    @objc dynamic var fullName:String {
        return "\(firstName) \(lastName)"
    }
    @objc private static let keyPathsForValuesAffectingFullName: Set<String> = [#keyPath(firstName), #keyPath(lastName)]
    
}

class MyController {
    
    let viewModel = MyViewModel()
    
    // KVO observer blocks need to be stronly retained somewhere.
    // this array serves this porpose.
    var observers = [NSKeyValueObservation]()
    
    init() {
        let nameObserver = viewModel.observe(\.firstName, options: [.initial, .new]) { (model, change) in
            print("nameObserver kicked in: \(change.newValue)")
        }
        let fullNameObserver = viewModel.observe(\.fullName, options: [.initial, .new]) { (model, change) in
            print("fullnameObserver kicked in \(change.newValue) \(self.viewModel.fullName)")
            print("s")
        }
        observers.append(nameObserver)
        observers.append(fullNameObserver)
    }
    
    func doStuff() {
        viewModel.firstName = "Sebastien"
        viewModel.lastName = "Windal"
    }
}

let myController = MyController()
myController.doStuff()