While there are a lot of talks how ReactiveCocoa is kind of a silver bullet that solves almost every problem you throw at it, most people still think of it as a magic black box. This talk is about the basic concepts how write your own ReactiveCocoa in Swift. It also features an in-depth look into Results, Promises and Signals. And I promise not to use the scary M-word. See by example how to implement a small app featuring networking, json parsing and table views using signals. Without black magic and by using great new language features like pattern matching, generics and the nice new closure syntax. All content of this talk is from the perspective of an object oriented developer, therefore no prerequisites are necessary. In the end you will be able to judge yourself if you want to go reactive by using ReactiveCocoa, your own framework or no reactivity at all.

1. How to use Functional
Reactive Programming
without Black Magic

2. let me = Person(name: "Jens Ravens")
@JensRavens
GitHub: JensRavens
nerdgeschoss.de
swift.berlin

3. A short introduction to
functional programming, the
universe and everything.

4. In the beginning McIlroy
created the unix pipe. And he
saw it was good.
ls | grep *.jpg | sort

5. Application Architecture

7. starting from a blank slate

8. implement to understand

9. And I promise not to use the
scary M-word.
me, 12 weeks ago.

10. How to train
your monad.

11. –Saunders Mac Lane
All told, a monad is just a monoid in the
category of endofunctors.
“

12. Monads are just Applicative Functors
“

13. ls | grep *.jpg | sort

14. Buy it, use it,
break it, fix it,
Trash it, change it,
mail - upgrade it.
– Daft Punk, Technologic

15. Buy it;
if error {
//TODO: Handle me!
} else {
use it;
if error {
//TODO: Handle me!
} else {
break it;
if error {
//TODO: Handle me!

16. ls | grep *.jpg | sort

17. Monad
something that defines map and bind

18. The optional Monad
let string: String? = "World"
let greeting = string.map{"Hello ($0)”}
//Hello World
extension Optional {
func bind<U> (f: T->U?) -> U? {
if let result = self.map({f($0)}) {
return result
} else {
return nil
}
}
}

19. The optional Monad
let string: String? = "World"
let greeting = string.map{"Hello ($0)”}
//Hello World
func greetOrNil(name: String)->String? {
if name == "World" {
return "Hello World"
} else {
return nil
}
}
let greeting2 = string.bind(greetOrNil)
//Hello World

20. The optional Monad
extension Optional {
func bind<U> (f: T->U?) -> U? {
if let result = self.map({f($0)}) {
return result
} else {
return nil
}
}
}
extension Optional {
func bind<U> (f: T->Optional<U>) -> Optional<U> {
switch self {
case let .Some(value): return f(value)
case .None: return nil
}
}
}

21. The result Monad
public enum Result<T> {
case Success(Box<T>)
case Error(NSError)
}

22. The result Monad
public enum Result<T> {
…
public func map<U>(f: T -> U) -> Result<U> {
switch self {
case let .Success(v):
return .Success(Box(f(v.value)))
case let .Error(error): return .Error(error)
}
}
…
}

23. The result Monad
public enum Result<T> {
…
public func bind<U>(f: T -> Result<U>)
-> Result<U> {
switch self {
case let .Success(v): return f(v.value)
case let .Error(error): return .Error(error)
}
}
…
}

24. ls | grep *.jpg | sort
Monad
Transform

25. func parseString(data: NSData) ->
Result<String>
func parseJson(data: NSData) ->
Result<[String: AnyObject]>
func asyncGreeting(name: String,
completion: Result<String>->Void)

26. public func bind<U>(f:(T, (Result<U>->Void))->Void)
-> (Result<U>->Void)->Void {
return { g in
switch self {
case let .Success(v): f(v.value, g)
case let .Error(error): g(.Error(error))
}
}
}

27. Interstellar

28. ls | grep *.jpg | sort

29. public final class Signal<T> {
private var value: Result<T>?
private var callbacks: [Result<T> -> Void] = []
public func subscribe(f: Result<T> -> Void) {
if let value = value {
f(value)
}
callbacks.append(f)
}
public func update(value: Result<T>) {
self.value = value
self.callbacks.map{$0(value)}
}
}

30. public func map<U>(f: T -> U) -> Signal<U> {
let signal = Signal<U>()
subscribe { result in
signal.update(result.map(f))
}
return signal
}
public func bind<U>(f: T -> Result<U>) -> Signal<U> {
let signal = Signal<U>()
subscribe { result in
signal.update(result.bind(f))
}
return signal
}

31. public func bind<U>(f: (T, (Result<U>->Void))->Void)
-> Signal<U> {
let signal = Signal<U>()
subscribe { value in
value.bind(f)(signal.update)
}
return signal
}

32. pushing instead of pulling

33. the rise of custom
operators

34. infix operator >>> { associativity left precedence 160 }
public func >>> <A,B> (left: Signal<A>,
right: A->Result<B>) -> Signal<B> {
return left.bind(right)
}
public func >>> <A,B>(left: Signal<A>,
right: (A, (Result<B>->Void))->Void) -> Signal<B>{
return left.bind(right)
}
public func >>> <A,B> (left: Signal<A>, right: A->B) ->
Signal<B> {
return left.map(right)
}

35. ls | grep *.jpg | sort

36. ls | grep *.jpg | sort
ls >>> grep("*.jpg") >>> sort

37. But what about
Threads?

38. public final class Thread {
public static func main<T>(a: T, completion:
T->Void) {
dispatch_async(dispatch_get_main_queue())
{
completion(a)
}
}
public static func background<T>(queue:
dispatch_queue_t)(_ a: T, _ completion: T->Void)
{
dispatch_async(queue){
completion(a)
}
}
}
ls >>> Thread.background(queue) >>> grep("*.jpg")
>>> sort >>> Thread.main

39. Extending UIKit to
support Signals.

40. var SignalHandle: UInt8 = 0
extension UITextField {
public var textSignal: Signal<String> {
let signal: Signal<String>
if let handle = objc_getAssociatedObject(self,
&SignalHandle) as? Signal<String> {
signal = handle
} else {
signal = Signal("")
NSNotificationCenter.defaultCenter().addObserver(self,
selector: Selector("textChanged:"), name:
UITextFieldTextDidChangeNotification, object: self)
objc_setAssociatedObject(self, &SignalHandle,
signal,
objc_AssociationPolicy(OBJC_ASSOCIATION_RETAIN_NONATOMIC))
}
return signal
}
public func textChanged(notification: NSNotification) {
textSignal.update(.Success(Box(self.text)))
}
}

41. If it’s variable, it qualifies
as a Signal.

42. ReactiveKitten
It’s about gifs. And cats.
And gifs of cats.

43. userTyping >>> createURL >>> loadRequest
>>> parseData >>> mainThread >>>
displayCats
The transform, the cat
and you.

44. import Interstellar
private func request(path: String, completion: Result<NSData>->Void)
{
let url = NSURL(string: baseURL.stringByAppendingString(path))!
let request = NSURLRequest(URL: url)
session.dataTaskWithRequest(request){ data, response, error in
if error != nil {
completion(.Error(error))
} else if let response = response as? NSHTTPURLResponse {
if response.statusCode >= 200 && response.statusCode<300 {
completion(.Success(Box(data)))
} else {
completion(.Error(NSError(domain: "Networking", code:
response.statusCode, userInfo: nil)))
}
} else {
completion(.Error(NSError(domain: "Networking", code: 500,
userInfo: nil)))
}
}.resume()
}

45. private func parseJSON(data: NSData)
->Result<[String: AnyObject]> {
var error: NSError?
if let json =
NSJSONSerialization.JSONObjectWithData(data, options:
nil, error: &error) as? [String: AnyObject] {
return .Success(Box(json))
} else {
return .Error(error!)
}
}

46. let imageSignal = gifSignal >>> getURL >>>
Thread.background >>> loadFromCache >>>
retryFromNetwork >>> Thread.main

47. class ViewController: UIViewController {
var signal: Signal<[Gif]>!
let searchBar = UISearchBar()
override func viewDidLoad() {
super.viewDidLoad()
navigationItem.titleView = searchBar
signal = searchBar.textSignal >>>
Network().search() >>> Thread.main

48. github.com/jensravens/reactivekitten

49. What’s next()?

50. Functors, Applicatives
and Monads in Pictures.
http://adit.io/posts/2013-04-17-
functors,_applicatives,_and_monads_in_pictures.html

51. The Introduction to RP
you’ve been missing.
https://gist.github.com/staltz/868e7e9bc2a7b8c1f754

52. ReactiveCocoa 3

53. RxSwift

54. Interstellar
available on Carthage
jensravens/interstellar

55. Thank you.
@JensRavens
github.com/jensravens/interstellar