Learn how to simplify the flow of data in your Swift application using a Flux / Redux / Elm like architecture inspired by functional programming. Check out jarsen/Reactor on github.

1. UNIDIRECTIONAL
DATA FLOW

2. WHAT IS THE STATE OF
YOUR APP?

3. WHERE DOES STATE LIVE?

4. WHAT DOES STATE LOOK
LIKE?

5. STATE
struct Player {
var name: String
var characterClass: CharacterClass
var maxHP: Int
var currentHP: Int
}

6. STATE COMPOSITION
struct RPGState {
var players: Player
var monsters: Monsters
// ...
}

7. (STATE) -> VIEW
UI AS A PURE FUNCTION OF STATE

8. REDRAW VIEW ON EVERY STATE
CHANGE?!?!?

9. REACT
✨ VIRTUAL DOM ✨

10. !
UIKIT

11. (STATE) -> VOID
(WITH SIDE EFFECTS)

12. extension ViewController {
func update(with state: State) {
nameLabel.text = state.name
}
}

13. CHANGING STATE

14. DATA FLOW
> Delegates
> Target-Actions
> Completion Blocks
> Notifications
> Segues
> didSet

15. WHAT DIRECTION IS THE
DATA FLOWING?

16. SPOT THE BUG!
class ViewController: UIViewController {
@IBOutlet var titleLabel: UILabel!
var name: String? {
didSet {
titleLabel.text = name
}
}
}

17. SPOT THE NEW BUG!
class ViewController: UIViewController {
@IBOutlet var titleLabel: UILabel?
var name: String? {
didSet {
titleLabel?.text = name
}
}
}

18. THE IMPLICITLY UNWRAPPED OPTIONAL DANCE
class ViewController: UIViewController {
@IBOutlet var titleLabel: UILabel?
var name: String? {
didSet {
configureView()
}
}
func configureView() {
titleLabel?.text = name
}
override func viewDidLoad() {
super.viewDidLoad()
configure()
}
}

19. SINGLE SOURCE
OF TRUTH™

20. JARSEN/REACTOR

21. REACTOR
> Holds the Single Source of Truth™
> Only the reactor can change the state
> Notifies all subscribers with state changes

23. Observing State
class ViewController: Reactor.Subscriber {
var reactor = App.sharedReactor
override func viewDidAppear(_ animated: Bool) {
super.viewDidAppear(animated)
reactor.add(subscriber: self)
}
override func viewDidDisappear(_ animated: Bool) {
super.viewDidDisappear(animated)
reactor.remove(subscriber: self)
}
func update(with state: State) {
nameLabel.text = state.name
}
}

24. UPDATING STATE
struct Increment: Event {}
extension ViewController {
@IBAction func didPressIncrement() {
reactor.perform(event: Increment())
}
}

25. ASYNC EVENTS
struct Update<T>: Event {
var value: T
}
class UserService {
// this type of function is also knows as an `EventEmitter`
func getUsers(state: State, reactor: Reactor<State>) -> Event? {
myNetworkThing.get("users") { json in
// transform to user object, using Marshal, of course
reactor.perform(event: Update(value: users))
}
}
}

26. ASYNC EVENTS
extension ViewController {
override func viewDidAppear(_ animated: Bool) {
super.viewDidAppear(animated)
reactor.add(subscriber: self)
reactor.perform(event: userService.getUsers)
}
}

27. HOW DO EVENTS UPDATE STATE?
extension State: StateType {
mutating func handle(event: Event) {
switch event {
case _ as LevelUp:
player.level += 1
default:
break
}
// also call `handle` on any substates
}
}

28. PERFORMANCE
CONCERNS

29. ROLL YOUR OWN
> Don't like the API?
> Don't like 3rd Party? !
It's a straightforward pattern.

30. NAVIGATION
STATE /
ROUTING

31. ENDLESS
POSSIBILITIES

32. MIDDLEWARE

33. OPTIMISTIC
NETWORK
RESULTS

34. TIME TRAVEL

35. STATE
RESTORATION

36. HOT RELOADINGUSING MARSHAL + KZFILEWATCHER

37. OTHER RESOURCES
> A composable pattern for pure state machines with
effects by Andy Matuschak
> Unidirectional Data Flow in Swift by Benjamin Encz
> Elmification of Swift
> MCV-N Swift Talk by Marcus Zarra
> Backend-driven Native UIs by John Sundell