Swift Summit San Francisco October 2015

Introduction to the ideas behind ReactiveCocoa, and why they're valuable.

Transcript

1. ASYNCHRONOUS CODE WITH REACTIVECOCOA
   1 — "Asynchronous Code with ReactiveCocoa" - Javier Soto. March 2015
   

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2. PREVIOUSLY, ON SWIFT SUMMIT...
   2 — "Asynchronous Code with ReactiveCocoa" - Javier Soto. March 2015
   

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3. FLASHBACK
   3 — "Asynchronous Code with ReactiveCocoa" - Javier Soto. March 2015
   

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4. BEFORE
   func loadAvatar(userID: String, completion: (UIImage?, NSError?) -> ()) {
   requestUserInfo(userID) { user, error in
   if let user = user {
   downloadImage(user.avatarURL) { avatar, error in
   if let avatar = avatar {
   completion(avatar, nil)
   } else {
   completion(nil, error)
   }
   }
   }
   else { completion(nil, error) }
   }
   }
   4 — "Asynchronous Code with ReactiveCocoa" - Javier Soto. March 2015
   

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5. AFTER
   func requestUserInfo(userID: String) -> Future
   func downloadImage(URL: NSURL) -> Future
   func loadAvatar(userID: String) -> Future {
   return requestUserInfo(userID)
   .map { $0.avatarURL }
   .andThen(downloadImage)
   }
   5 — "Asynchronous Code with ReactiveCocoa" - Javier Soto. March 2015
   

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6. WHY?
   6 — "Asynchronous Code with ReactiveCocoa" - Javier Soto. March 2015
   

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7. ASYNCHRONY IN MOBILE APPLICATIONS
   > KVO
   > User data
   > Networking
   > Gesture recognizers
   > Animations
   > Sensors
   > Mutable State
   > ...
   7 — "Asynchronous Code with ReactiveCocoa" - Javier Soto. March 2015
   

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8. 8 — "Asynchronous Code with ReactiveCocoa" - Javier Soto. March 2015
   

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9. TL;DR
   ASYNCHRONOUS CODE IS HARD
   9 — "Asynchronous Code with ReactiveCocoa" - Javier Soto. March 2015
   

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10. ASYNCHRONOUS CODE IS HARD
    > Cancelation
    > Throttling
    > Error handling
    > Retrying
    > Threading
    > ...
    10 — "Asynchronous Code with ReactiveCocoa" - Javier Soto. March 2015
    

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11. ''THERE HAS TO BE
    A BETTER WAY!''
    11 — "Asynchronous Code with ReactiveCocoa" - Javier Soto. March 2015
    

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12. That perfection is unattainable is
    no excuse not to strive for it.
    — Stolen from Nacho's Twitter bio
    12 — "Asynchronous Code with ReactiveCocoa" - Javier Soto. March 2015
    

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13. REACTIVECOCOA™
    13 — "Asynchronous Code with ReactiveCocoa" - Javier Soto. March 2015
    

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14. REACTIVECOCOA
    IS HARD
    14 — "Asynchronous Code with ReactiveCocoa" - Javier Soto. March 2015
    

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15. REACTIVECOCOA IS HARD
    > Syntax is unfamiliar
    > Foreign concepts
    > Feels different to traditional Cocoa APIs
    > Apple's APIs don't use it.
    15 — "Asynchronous Code with ReactiveCocoa" - Javier Soto. March 2015
    

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16. REACTIVECOCOA IS SIMPLE1
    > Few concepts
    > Abstract away complexity
    > One pattern for asynchronous APIs
    1 ''Simple made Easy'' - Rich Hickey
    16 — "Asynchronous Code with ReactiveCocoa" - Javier Soto. March 2015
    

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17. 17 — "Asynchronous Code with ReactiveCocoa" - Javier Soto. March 2015
    

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18. CONCEPTS IN COCOA INVOLVED IN ASYNCHRONOUS APIS
    > Delegation
    > NSOperation
    > NSNotificationCenter
    > KVO
    > Target-Action
    > Responder chain
    > Callback blocks
    18 — "Asynchronous Code with ReactiveCocoa" - Javier Soto. March 2015
    

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19. SIGNALS
    19 — "Asynchronous Code with ReactiveCocoa" - Javier Soto. March 2015
    

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20. SIGNALS
    > Next
    > Failed
    > Completed
    > Interrupted
    20 — "Asynchronous Code with ReactiveCocoa" - Javier Soto. March 2015
    

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21. Signal
    AND
    SignalProducer
    21 — "Asynchronous Code with ReactiveCocoa" - Javier Soto. March 2015
    

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22. Signal VS SignalProducer
    func doSomethingAndGiveMeTheResult() -> SignalProducer
    func observeSomeOnGoingWork() -> Signal
    22 — "Asynchronous Code with ReactiveCocoa" - Javier Soto. March 2015
    

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23. OPERATORS
    23 — "Asynchronous Code with ReactiveCocoa" - Javier Soto. March 2015
    

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24. RAC'S OPERATORS: DECLARATIVE VS IMPERATIVE
    let array = ["one", "two", "three"]
    // Imperative
    var newArray: [String] = []
    for string in array {
    newArray.append(string.uppercaseString)
    }
    // Declarative
    let newArray = array.map { string in return string.uppercaseString }
    24 — "Asynchronous Code with ReactiveCocoa" - Javier Soto. March 2015
    

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25. RAC'S OPERATORS: DECLARATIVE VS IMPERATIVE
    let throttleInterval: NSTimeInterval = 0.5
    // Imperative
    func search(query: String, completion: ([SearchResult]?, MyErrorType?) -> ())
    var lastSearch: NSDate? // <--- State
    func didTypeSearchQuery(searchQuery: String) {
    guard (lastSearch?.timeIntervalSinceNow > throttleInterval) ?? false else { return }
    lastSearchDate = NSDate()
    search(searchQuery) { results, error in ... }
    }
    // Declarative
    let searchQuerySignal: Signal
    func search(query: String) -> SignalProducer<[SearchResult], MyErrorType>
    searchQuerySignal.throttle(throttleInterval).flatMap(.Latest, search)
    25 — "Asynchronous Code with ReactiveCocoa" - Javier Soto. March 2015
    

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26. OPERATORS
    > map
    > filter
    > reduce
    > collect
    > combineLatest
    > zip
    > merge / concat / switchToLatest
    > flatMapError / mapError
    > retry
    > throttle
    26 — "Asynchronous Code with ReactiveCocoa" - Javier Soto. March 2015
    

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27. KVO
    27 — "Asynchronous Code with ReactiveCocoa" - Javier Soto. March 2015
    

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28. KVO
    > Crash if object deallocates while being observed.
    > Crash if observe wrong keypath (stringly-typed API)
    > Possible crash when de-registering
    > Easy to break parent class (context often misused)
    > All observations come through one method
    > Lose contract: "is this KVO-compliant?"
    28 — "Asynchronous Code with ReactiveCocoa" - Javier Soto. March 2015
    

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29. PROPERTY
    29 — "Asynchronous Code with ReactiveCocoa" - Javier Soto. March 2015
    

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30. PROPERTY
    // KVO
    class MyClass {
    private(set) dynamic var value: Type
    }
    let object = MyClass()
    object.addObserver(self, forKeyPath: "value", options: [], context: ctx)
    func observeValueForKeyPath(keyPath: String?,
    ofObject object: AnyObject?,
    change: [NSObject : AnyObject]?,
    context: UnsafeMutablePointer) { /* HAVE FUN!! */ }
    // PropertyType
    class MyClass {
    var value: AnyProperty
    }
    let object = MyClass()
    object.value.producer.startWithNext { value in ... }
    30 — "Asynchronous Code with ReactiveCocoa" - Javier Soto. March 2015
    

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31. MYTH:
    "TO USE REACTIVECOCOA, I NEED
    TO RE-WRITE MY WHOLE APP"
    31 — "Asynchronous Code with ReactiveCocoa" - Javier Soto. March 2015
    

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32. CONCLUSIONS
    > Our tools are imperfect. Strive to reconsider patterns,
    seek better alternatives.
    > There's value in these abstractions.
    > ReactiveCocoa can be adopted slowly.
    32 — "Asynchronous Code with ReactiveCocoa" - Javier Soto. March 2015
    

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33. REFERENCES
    > ReactiveCocoa: https://github.com/ReactiveCocoa/ReactiveCocoa
    > Back to the Futures - Me: https://realm.io/news/swift-summit-
    javier-soto-futures
    > Functional Reactive Programming
    in an Imperative World - Nacho Soto: https://realm.io/news/
    nacho-soto-functional-reactive-programming
    > "Simple made Easy" - Rich Hickey: http://www.infoq.com/
    presentations/Simple-Made-Easy
    33 — "Asynchronous Code with ReactiveCocoa" - Javier Soto. March 2015
    

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34. THANK YOU!
    34 — "Asynchronous Code with ReactiveCocoa" - Javier Soto. March 2015
    

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