RAC3, A Real World Use Case (aka ReactiveChess)

Overview of how WatchChess was implemented using ReactiveCocoa 3.0, sharing a few tricks that I learned during its development.

Transcript

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

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

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3. 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
   

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4. Reac%veChess - Javier Soto, RACDC 2015 4
   

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

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6. 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
   

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7. Big Takeaways
   • Typed Signals
   • Less debugging required
   • Conciseness
   • Clearer seman8cs
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8. 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.");
   }];
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9. 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.") })
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10. Biggest sources of frustra.on
    • Compiler crashes
    • Type errors
    Reac%veChess - Javier Soto, RACDC 2015 10
    

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

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12. Type Errors
    WAT
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13. Type Errors
    Extract intermediate results into separate values
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14. Type Errors
    Inspect the types (⌥ + click)
    Reac%veChess - Javier Soto, RACDC 2015 14
    

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

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16. Type Errors
    Check RAC's func.on signatures (⌘ + click)
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17. Type Errors
    Check if your types match those expected by RAC
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18. Type Errors
    Look for a func+on that matches what you're trying to do
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19. Type Errors
    If it compiles, it works.
    Reac%veChess - Javier Soto, RACDC 2015 19
    

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

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

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22. ChessAPI.swift
    import ReactiveCocoa
    import Argo
    func tournaments() -> SignalProducer<[Tournament], APIError> {
    return self.JSONWithPath("/tournaments")
    |> attemptMap(extractJSONKey("tournaments"))
    |> attemptMap(extractJSONObjects)
    |> reverse
    }
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23. 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)
    }
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24. 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
    

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25. Custom RAC Operators
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26. Custom RAC Operators
    return self.urlSession.rac_dataWithRequest(request)
    |> log(started: "Started: \(URL)",
    completed: "Finished: \(URL)")
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27. 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
    

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28. 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
    

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29. 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
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30. Custom RAC Operators
    return self.urlSession.rac_dataWithRequest(request)
    |> log(started: "Started: \(URL)",
    completed: "Finished: \(URL)")
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31. 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
    

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32. 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
    

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

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34. 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
    

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

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

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37. Ques%ons?
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