Be Proactive: Use Reactive

What is “functional reactive programming?” Why should you use it? This talk is a high-level, easy-to-grasp intro to the core concepts behind reactive programming.

A video of this talk is available: https://vimeo.com/125191686

And speakers' notes, etc. are on my blog: https://www.dzombak.com/talks/2015-04-be-proactive-use-reactive.html

Transcript

1. BE PROACTIVE USE REACTIVE
2. iOS @ NY Times @cdzombak github.com/cdzombak chris dzombak dzombak@nytimes.com
3. What is reactive programming?
4. “ ” reactive |rēˈaktiv| … a programming paradigm oriented around data flows and the propagation of change
9. reactive programming data flows propagation of change =
11. we all respond to flowing data and react to changes Model View Controller
12. Cocoa’s KVO? NSNotificationCenter? Ember or Angular observers? Callbacks? Listeners? How is this different from… Programming?
13. Back to the basics
14. Subject Observer notify()
15. DATA STREAMS
16. Data type a value over time
17. •updated property values •mouse cursor position •typing characters into a text field •database records
18. •updated property values •mouse cursor position •typing characters into a text field •database records
19. Collection of emitted events ordered in time
20. with functions for observation
22. onNext( )
23. onNext( )
24. onNext( )
25. onComplete()
27. onNext( )
28. onNext( )
29. onError() x
30. [ "value”, "other value”, "another value” ]
31. [ "value”, "other value”, "another value” ] "a value",
32. [ "value”, "other value”, "another value” ] "a value", "other value",
33. [ "value”, "other value”, "another value” ] "a value", "other value", "another value"
34. textField.rac_textSignal() .subscribeNext({ (value) -> Void in // value = “H”, “He”, … })
35. textField.rac_textSignal() .subscribeNext({ (value) -> Void in // value = “H”, “He”, … })
36. apiClient.performRequest(request) .subscribeNext({ (response) -> Void in // do something with response }, error: { (error) -> Void in println(“Error: \(error)”) }, completed: { () -> Void in println(“Done.”) })
37. Stream.transform(f: (x) -> y) -> Stream Streams are composable
38. 1 3 2 2 6 4 map { (x) -> Int in x * 2 } Streams are composable
39. 1 2 4 filter { (x) -> Bool in x % 2 == 0 } 4 2 Streams are composable
40. Double tap! Demo
43. taps .bufferWithTime(0.5) .map { ($0 as RACTuple).count } .filter { ($0 as Int) == 2 } .subscribeNext { (_) in println("Double tap!") }
44. taps .bufferWithTime(0.5) .map { ($0 as RACTuple).count } .filter { ($0 as Int) == 2 } .subscribeNext { (_) in println("Double tap!") }
45. taps .bufferWithTime(0.5) .map { ($0 as RACTuple).count } .filter { ($0 as Int) == 2 } .subscribeNext { (_) in println("Double tap!") }
46. 1 2 3 taps .bufferWithTime(0.5) .map { ($0 as RACTuple).count } .filter { ($0 as Int) == 2 } .subscribeNext { (_) in println("Double tap!") }
47. 2 taps .bufferWithTime(0.5) .map { ($0 as RACTuple).count } .filter { ($0 as Int) == 2 } .subscribeNext { (_) in println("Double tap!") }
48. taps .bufferWithTime(0.5) .map { ($0 as RACTuple).count } .filter { ($0 as Int) == 2 } .subscribeNext { (_) in println("Double tap!") } Double tap!
49. RACSignal.combineLatest([ slowToEmitStream, evenSlowerToEmitStream, ]) .doNext { let tuple = $0 as RACTuple processResults( tuple.first, tuple.second) } .deliverOn(RACScheduler.mainThreadScheduler()) .subscribeCompleted { () -> Void in println("The work is done!") }
50. MODEL WITH STREAMS
51. MODEL WITH STREAMS BUT…WHY?
52. Claim code should communicate intent
53. Current tooling is insufficient
54. map extension Array { func map<U>(transform: (T) -> U) -> [U] }
55. let input = [1, 2, 3] var output = [Int]() for number in input { output.append(number * 2) } // output: [2, 4, 6] let output = [1, 2, 3].map { $0 * 2 } // output: [2, 4, 6]
56. let input = [1, 2, 3] var output = [Int]() for number in input { output.append(number * 2) } // output: [2, 4, 6] let output = [1, 2, 3].map { $0 * 2 } // output: [2, 4, 6] Concept: 1-1 mapping
57. map reifies 1-1 data transformation
58. Good Thing™ reify |ˈrēəәˌfī| make (something abstract) more concrete or real
59. reactive programming reifies event-driven software
62. var count = 0 upButton.addTarget(self, action: “upButtonTouched:”, forControlEvents: .TouchUpInside) downButton.addTarget(self, action: “downButtonTouched:", forControlEvents: .TouchUpInside) countLabel.text = String(count) func upButtonTouched(sender: UIButton) { count++ countLabel.text = String(count) } func downButtonTouched(sender: UIButton) { count-- countLabel.text = String(count) }
63. let upTaps = upButton .rac_signalForControlEvents(.TouchUpInside) let downTaps = downButton .rac_signalForControlEvents(.TouchUpInside) let count = RACSignal.merge([ RACSignal.return(0), upTaps.mapReplace(1), downTaps.mapReplace(-1) ]) .scanWithStart(0, reduce: { $0 + $1 }) .map { String($0) } count ~> RAC(self, "countLabel.text")
64. client.loginWithSuccess({ client.loadCachedTweetsWithSuccess({ (tweets) in client.fetchTweetsAfterTweet(tweets.last, success: { (tweets) -> Void in // Now we can show our tweets }, failure: { (error) -> Void in presentError(error) }) }, failure: { (error) -> Void in presentError(error) }) }, failure: { (error) -> Void in presentError(error) })
65. client.login() .then { return client.loadCachedTweets() } .flattenMap { (tweets) -> RACStream in return client.fetchTweetsAfterTweet(tweets.last) } .subscribeError({ (error) -> Void in presentError(error) }, completed: { () -> Void in // Now we can show our tweets })
66. bring changes over time into your type system
67. /// Clients should observe via property observer: public var title: String public let title: Signal<String, NoError>
68. func loginWithSuccess( success: () -> Void, failure: (NSError) -> Void) { // function doesn’t return anything // it jumps into two callbacks based on return } func login() -> RACSignal { // function has a native return value // a data stream object that we can observe }
69. becomes easier concurrency
70. Scheduler 
 schedules when and where work is performed
 
 reactive concurrency
71. Scheduler 
 schedules when and where work is performed
 
 deliverOn(Scheduler) subscribeOn(Scheduler) reactive concurrency
72. SO… HOW DO I DO THIS? (photo by Andrew Sardone)
73. ReactiveCocoa ReactiveExtensions RxJava Bacon.js Elm github.com/ReactiveCocoa/ReactiveCocoa github.com/Reactive-Extensions github.com/ReactiveX/RxJava github.com/baconjs/bacon.js elm-lang.org
74. SOURCES FURTHER READING
75. Missing RX Intro Input & Output RxMarbles Other j.mp/missingrxintro j.mp/joshaberio rxmarbles.com pinboard.in/u:cdzombak/t:reactiveprogramming
76. B Y E (photo by Chris Dzombak) (puppy by Shane Bliemaster)