Everyday Reactive (try! Swift Tokyo '17)

This is my talk from try! Swift Tokyo exploring tips and tricks for determining when reactive programming can be a potent tool, as well as scenarios to avoid that might threaten code quality and performance. The talk's focus is on concepts in reactive programming, the code shows off different Swift reactive implementations.

https://www.tryswift.co/tokyo/

Transcript

1. EVERYDAY REACTIVE 毎⽇日リアクティブ Agnes Vasarhelyi @vasarhelyia
 ! Ustream (IBM Cloud Video)
3. "Reactive programming manages asynchronous data flows between sources of data and components that need to react to that data." MATT GALLAGHER, COCOAWITHLOVE.COM
4. • Reduces state • Less, but more concise code • Easier to read
5. IS THERE A FRAMEWORK FOR THAT? There are plenty.
7. WHEN DO I APPLY IT? Depends on complexity.
8. WHERE DO I APPLY IT? • MVVM • async ops
9. OBSERVATION
10. let (signal, observer) = Signal<String, NoError>.pipe() signal.observeValues { animal in print( "value: \(animal)") } observer.sendNext(value: "") observer.sendNext(value: "") > value: > value: ReactiveSwift (RAC)
11. LET'S REDUCE SOME STATE
12. var loading: Bool var userLoggedIn: Bool var didShowAlert: Bool var loading = reactive(userLoggedIn) && reactive(didShowAlert) 23 STATE 22 STATE
13. TRANSFORM / COMBINE
14. let userLoggedIn = PublishSubject<Bool>() let didLoadContent = PublishSubject<Bool>() let loading = Observable.combineLatest(userLoggedIn, didLoadContent) { !($0 && $1) } loading.subscribe(onNext: { print("loading: \($0)") }) userLoggedIn.onNext(false) didLoadContent.onNext(false) userLoggedIn.onNext(true) didLoadContent.onNext(true) > loading: true > loading: true > loading: false RxSwift
15. SIMPLIFY / UNIFY ASYNC OPERATIONS
16. let catButton = UIButton(title: "") let url = URL(string: "http://catfacts-api.appspot.com/api/facts? number=1") let catFact = URLSession.shared.rx.json(url:url!) .map( { return "\(parsedCatFact($0))" }) Observable.combineLatest(catButton.rx.tap, catFact) { c, fact in "\(c) \(fact)" }.subscribe(onNext: { print("\($0)") }) > : Cats can be right-pawed or left-pawed. > : In 1987 cats overtook dogs as the number one pet in America. RxSwift
17. TRADE-OFFS, COMPLICATIONS
18. 1. DEBUGGING
19. HOW TO HELP IT?
20. func logAnimals() { let animal = MutableProperty<String>("") let animalStream = animal.producer.logEvents(identifier: "") animalStream.start() animal.value = "" } [] starting fileName: (...)/A.swift, functionName: logAnimals(), lineNumber: 16 [] value fileName: (...)/A.swift, functionName: logAnimals(), lineNumber: 16 [] started fileName: (...)/A.swift, functionName: logAnimals(), lineNumber: 16 [] value fileName: (...)/A.swift, functionName: logAnimals(), lineNumber: 16 ... ReactiveSwift (RAC)
21. 2. "FANCY KVO"
22. viewModel.title.observeNext { [weak self] v in self?.titleLabel.text = v self?.refreshButton.enabled = true self?.canRefresh = true }) func update() { if (!self.canRefresh) return; ... } Bond
23. viewModel.title.bind(to: titleLabel) Bond
24. viewModel.title.map { n -> Bool in return n != nil }.bind(to: refreshButton.reactive.isEnabled) Bond
25. viewModel.title.bind(to: titleLabel) viewModel.title .bidirectionalBind(to: titleTextField.reactive.bnd_text) Bond
26. 3. INJECT SIDE EFFECTS CAREFULLY
27. let catFact = URLSession.shared.rx.json(url:url!) .map( { return "\(parsedCatFact($0))" }) .do(onNext: { _ in print("EFFECT") }) catFact.subscribe(onNext: { print("1. : \($0)") }) catFact.subscribe(onNext: { print("2. : \($0)") }) > EFFECT > 1. : Most cats adore sardines. > EFFECT > 2. : Cats take between 20-40 breaths per minute. RxSwift
28. ... .do(onNext: { fact in Analytics.trackEvent("cat fact generated: \(fact)") })
29. 4. AVOID CHAOS
30. Thread 1 eraseButton.reactive.tap.onNext( { stateManager.items.remove($0) }) Thread 2 apiResponse.onNext ( { stateManager.items.append($0) }) eraseButton.reactive.tap.onNext( { stateManager.removeItem($0) }).onScheduler(MainScheduler) apiResponse.onNext ( { stateManager.appendItem($0) }).onScheduler(BackgroundScheduler) immutability + schedulers =
32. ... .ignoreNil() .flatMapLatest { $0.unwrap } .collect() .first() .filter(include: { s -> Bool in return s.characters.count > 3 }) .merge(with: offlineSignal.distinct()) .combineLatest(with: viewModel.title.map { t -> Bool in return t != nil }).bind(to: refreshButton.reactive.isEnabled)
33. NO MORE 
 IMPERATIVE?
34. DESIGNING APIS • don't expose reactive, • support it
35. THANKS
 @vasarhelyia
36. RESOURCES https://github.com/ReactiveKit/Bond https://github.com/ReactiveX/RxSwift https://github.com/ReactiveCocoa/ReactiveCocoa https://github.com/mattgallagher/CwlSignal https://www.cocoawithlove.com/blog/reactive-programming-what-and-why.html https://www.youtube.com/watch?v=7AqXBuJOJkY https://speakerdeck.com/joshaber/better-code-for-a-better-world Photos from unsplash.com