RAC3, A Real World Use Case aka Reac%veChess Reac%veChess - Javier Soto, RACDC 2015 1

Javier Soto (@Javi) iOS at Twi)er Reac%veChess - Javier Soto, RACDC 2015 2

Predic'on: All of the code in these slides won't compile on the latest Xcode by the 6me you're reading this. Reac%veChess - Javier Soto, RACDC 2015 3

Reac%veChess - Javier Soto, RACDC 2015 4

WatchChess.app Reac%veChess - Javier Soto, RACDC 2015 5

WatchChess.app • Reac&veCocoa 3.0 • Argo History • First prototype: Swi/ 1.2 with Xcode 6.3 Beta 1 • v1.0: Swi/ 1.1, RAC 3.0 pre-alpha • v1.1: Swi/ 1.2, RAC 3.0-beta.1 • v1.2: RAC 3.0-beta.6 Reac%veChess - Javier Soto, RACDC 2015 6

Big Takeaways • Typed Signals • Less debugging required • Conciseness • Clearer seman8cs Reac%veChess - Javier Soto, RACDC 2015 7

Conciseness [[[[client logInUser] flattenMap:^(User *user) { return [client loadCachedMessages:user]; }] flattenMap:^(NSArray *messages) { return [client fetchMessagesAfter:messages.lastObject]; }] subscribeNext:^(NSArray *newMessages) { NSLog(@"New messages: %@", newMessages); } completed:^{ NSLog(@"Fetched all messages."); }]; Reac%veChess - Javier Soto, RACDC 2015 8

Conciseness client.loginUser() |> flatMap(.Latest) { client.loadCachedMessages($0) } |> flatMap(.Concat) { client.fetchMessagesAfter($0.last) } |> start(next: { println("New messages: \($0)") }, completed: { println("Fetched all messages.") }) Reac%veChess - Javier Soto, RACDC 2015 9

Biggest sources of frustra.on • Compiler crashes • Type errors Reac%veChess - Javier Soto, RACDC 2015 10

Figure out type errors in RAC 3 with this one weird trick Reac%veChess - Javier Soto, RACDC 2015 11

Type Errors WAT Reac%veChess - Javier Soto, RACDC 2015 12

Type Errors Extract intermediate results into separate values Reac%veChess - Javier Soto, RACDC 2015 13

Type Errors Inspect the types (⌥ + click) Reac%veChess - Javier Soto, RACDC 2015 14

Type Errors Inspect the types (⌥ + click) Reac%veChess - Javier Soto, RACDC 2015 15

Type Errors Check RAC's func.on signatures (⌘ + click) Reac%veChess - Javier Soto, RACDC 2015 16

Type Errors Check if your types match those expected by RAC Reac%veChess - Javier Soto, RACDC 2015 17

Type Errors Look for a func+on that matches what you're trying to do Reac%veChess - Javier Soto, RACDC 2015 18

Type Errors If it compiles, it works. Reac%veChess - Javier Soto, RACDC 2015 19

ChessAPI.swift Reac%veChess - Javier Soto, RACDC 2015 20

ChessAPI.swift enum APIError: ErrorType { case NetworkError(NSError) case JSONParsingError(NSError) case InvalidJSONStructure(reason: String) } Reac%veChess - Javier Soto, RACDC 2015 21

ChessAPI.swift import ReactiveCocoa import Argo func tournaments() -> SignalProducer<[Tournament], APIError> { return self.JSONWithPath("/tournaments") |> attemptMap(extractJSONKey("tournaments")) |> attemptMap(extractJSONObjects) |> reverse } Reac%veChess - Javier Soto, RACDC 2015 22

ChessAPI.swift func JSONWithPath(path: String) -> SignalProducer { let request = APIRequestWithPath(path) let URL = request.URL return self.urlSession.rac_dataWithRequest(request) |> log(started: "Started: \(URL)", completed: "Finished: \(URL)") |> mapError { APIError.NetworkError($0) } |> map { $0.0 } |> attemptMap(parseJSON) } Reac%veChess - Javier Soto, RACDC 2015 23

ChessAPI.swift func parseJSON(data: NSData) -> Result { var error: NSError? if let json = NSJSONSerialization(data, error: &error) { return success(JSON.parse(json)) } else { return failure(APIError.JSONParsingError(error!)) } } Reac%veChess - Javier Soto, RACDC 2015 24

Custom RAC Operators Reac%veChess - Javier Soto, RACDC 2015 25

Custom RAC Operators return self.urlSession.rac_dataWithRequest(request) |> log(started: "Started: \(URL)", completed: "Finished: \(URL)") Reac%veChess - Javier Soto, RACDC 2015 26

Custom RAC Operators log(): func log(started: String = "", next: String = "", completed: String = "") (producer: SignalProducer) -> SignalProducer { return producer |> on(started: { println(started) }, next: { println(next + " \($0)") }, completed: { println(completed) }) } Reac%veChess - Javier Soto, RACDC 2015 27

Custom RAC Operators log(): func log(started: String = "", next: String = "", completed: String = "") (producer: SignalProducer) -> SignalProducer (String, String, String) -> SignalProducer -> SignalProducer Reac%veChess - Javier Soto, RACDC 2015 28

Custom RAC Operators log(): (String, String, String) -> SignalProducer -> SignalProducer log("someMessage"): SignalProducer -> SignalProducer |>: (SignalProducer, (SignalProducer -> SignalProducer)) -> SignalProducer // Infix order would be... // SignalProducer |> (SignalProducer -> SignalProducer) -> SignalProducer Reac%veChess - Javier Soto, RACDC 2015 29

Custom RAC Operators return self.urlSession.rac_dataWithRequest(request) |> log(started: "Started: \(URL)", completed: "Finished: \(URL)") Reac%veChess - Javier Soto, RACDC 2015 30

WatchKit Controllers import WatchKit class TournamentsInterfaceController: WKInterfaceController { private let tournaments = MutableProperty<[Tournament]>([]) override init() { super.init() self.tournaments.producer |> skip(1) |> skipRepeatedArrays |> start(next: { [unowned self] tournaments in self.updateUIWithTournaments(tournaments) }) } override func willActivate() { self.tournaments <~ self.chessAPI.requestTournaments() |> printAndFilterErrors("Error requesting tournaments") |> observeOn(UIScheduler()) } } Reac%veChess - Javier Soto, RACDC 2015 31

WatchKit Controllers self.tournaments <~ self.chessAPI.requestTournaments() // To bind to a property, the signal can't send errors. |> printAndFilterErrors("Error requesting tournaments") } Reac%veChess - Javier Soto, RACDC 2015 32

printAndFilterErrors() func printAndFilterErrors) -> Signal { return signal |> on(error: { println("\(message): \($0)") }) |> catch { SignalProducer.empty } } Reac%veChess - Javier Soto, RACDC 2015 33

WatchKit Controllers self.tournaments.producer // Easy optimization to minimize Bluetooth round-trips. |> skipRepeatedArrays |> start(next: { [unowned self] tournaments in self.updateUIWithTournaments(tournaments) }) Reac%veChess - Javier Soto, RACDC 2015 34

skipRepeatedArrays() public func skipRepeatedArrays(signal: Signal<[T], E>) -> Signal<[T], E> { return signal |> skipRepeats(==) } Reac%veChess - Javier Soto, RACDC 2015 35

THANKS • Jus%n Spahr-Summers (@jspahrsummers) • Nacho Soto (@NachoSoto) • You Reac%veChess - Javier Soto, RACDC 2015 36

Ques%ons? Reac%veChess - Javier Soto, RACDC 2015 37