Continuation-Passing Style and Design By Contract(English ver.) / 20190319(E) #tryswift_pre

Presentation in
【増枠/increase】try! Swift Pre Talks 2019 - connpass
https://tryswifttokyo-aftertalks.connpass.com/event/120987/

Japanese ver.
https://speakerdeck.com/takasek/20190319-number-tryswift-pre

Transcript

1. Continuation-Passing Style and Design
   By Contract
   by.
   2019/3/19 try! Swift Pre Talks 2019
   1
   

   View Slide

2. takasek
   @takasek
   Works
   OSS: ActionClosurable౳
   App: PasteTheType
   Articles
   ʮίϯύΠϧΤϥʔ΍ϥϯλΠϜΤϥʔΛ௚͍ͯ͘͠
   ͚ͩͰiOSΞϓϦͷ࡞Γํ͕Θ͔ΔϓϩδΣΫτʯ
   ʮ͓લΒ͕ModelͱݺͿΞϨΛͳΜͱݺͿ΂͖͔ʯ
   ʮiOSΞϓϦઃܭύλʔϯೖ໳ʯʢڞஶʣ
   2
   

   View Slide

3. ʮiOSΞϓϦઃܭύλʔϯೖ໳ʯ
   ON SALE!!
   https://peaks.cc/takasek/iOS_architecture
   takasek୲౰ষ
   Chap 1ʮTo designʯ
   Chap 2ʮBefore applying patterns to your
   designʯ
   Chap 3ʮDesigning swiftyʯ
   Chap 4ʮOverview through history of
   architecturesʯ
   3
   

   View Slide

4. Continuation-
   Passing Style
   (CPS)
   4
   

   View Slide

5. // Without CPS
   func doSomething(i: Int) -> String {
   sleep(100)
   return "\(i)"
   }
   // With CPS
   func doSomething(i: Int, completion: @escaping (String) -> Void) {
   DispatchQueue.global().async {
   sleep(100)
   completion("\(i)")
   }
   }
   5
   

   View Slide

6. !
   6
   

   View Slide

7. func doSomething(
   i: Int,
   completion: @escaping (String) -> Void
   )
   This interface isn't the best
   7
   

   View Slide

8. ʮI know what you meanʯ
   8
   

   View Slide

9. ʮAbout Callback Hell, huh?ʯ
   9
   

   View Slide

10. Nop.
    10
    

    View Slide

11. Design
    By Contract
    11
    

    View Slide

12. Design By Contract
    The idea to construct reliable
    system
    introduced by Bertrand Meyer
    12
    

    View Slide

13. Design By Contract
    Asserts;
    • Preconditionɿ
    a caller should ensure it.
    described by Argument Type or so on.
    • Postconditionɿ
    a callee should ensure it.
    described by Return Type or so on.
    If precondition is violated, throw Exception.
    13
    

    View Slide

14. For example,
    func half(of i: Int) throws -> Int {
    assert(i.isMultiple(of: 2))
    if !i.isMultiple(of: 2) { throw Error.isOdd }
    return i / 2
    }
    • Precondition:
    • accepts Int.
    • accepts Even. (not describable as type)
    • Postcondition: returns Int.
    • Exception: thrown if the argument is odd.
    14
    

    View Slide

15. Swifty type system helps Design by Contract.
    15
    

    View Slide

16. By the way,
    16
    

    View Slide

17. func half(of i: Int) throws -> Int {
    if !i.isMultiple(of: 2) {
    throw Error.isOdd
    }
    return i / 2
    }
    translate it to CPS.
    17
    

    View Slide

18. func half(of i: Int, completion: (Int) -> Void) {
    if !i.isMultiple(of: 2) {
    return
    }
    completion(i / 2)
    }
    18
    

    View Slide

19. View Slide

20. OK, in the case of Odd
    value...?
    20
    

    View Slide

21. View Slide

22. Not called...?
    22
    

    View Slide

23. View Slide

24. completion
    hadn't be called
    24
    

    View Slide

25. func half(of i: Int, completion: (Int) -> Void) {
    if !i.isMultiple(of: 2) {
    return //
    !
    }
    completion(i / 2)
    }
    25
    

    View Slide

26. enum Result {
    case success(T)
    case error(Error)
    }
    func half(of i: Int, completion: (Result) -> Void) {
    if !i.isMultiple(of: 2) {
    return //
    !
    }
    completion(.success(i / 2))
    }
    26
    

    View Slide

27. enum Result {
    case success(T)
    case error(Error)
    }
    func half(of i: Int, completion: (Result) -> Void) {
    if !i.isMultiple(of: 2) {
    completion(.error(.isOdd)) //
    }
    completion(.success(i / 2))
    }
    27
    

    View Slide

28. Okay, check again!
    28
    

    View Slide

29. View Slide

30. Called twice...?
    30
    

    View Slide

31. func half(of i: Int, completion: (Result) -> Void) {
    if !i.isMultiple(of: 2) {
    completion(.error(.isOdd))
    //
    !
    }
    completion(.success(i / 2))
    }
    31
    

    View Slide

32. func half(of i: Int, completion: (Result) -> Void) {
    if !i.isMultiple(of: 2) {
    completion(.error(.isOdd))
    return //
    !
    }
    completion(.success(i / 2))
    }
    32
    

    View Slide

33. CPS avoids
    benefits of
    Static Typing
    33
    

    View Slide

34. ͳͥͳͷ͔
    ໭Γ஋ͷܕʹΑͬͯ
    ࣄޙ৚݅ΛදݱͰ͖ͳ͍͔Β
    (T, (U) -> Void) -> Void
    Void͸࠷ऑͷࣄޙ৚݅
    34
    

    View Slide

35. Ͳ͏͢Ε͹͍͍͔
    ໭Γ஋ͷܕʹΑͬͯ
    ࣄޙ৚݅Λදݱ͢Ε͹͍͍
    (T) -> XXX
    ʮ͍ͣΕ݁Ռ͕ಘΒΕΔʯ͜ͱΛܕ෇͚ͰࣔͤΕ͹ɺ
    ඇಉظॲཧͰ΋໭Γ஋Λػೳͤ͞ΒΕΔ
    35
    

    View Slide

36. func half(of i: Int) -> RxSwift.Single {
    if !i.isMultiple(of: 2) {
    return .error(Error.isOdd)
    }
    return .just(i / 2)
    }
    ͜ΕͳΒ੩తܕ෇͚ͷԸܙΛड͚ͭͭɺ
    ʮඇಉظͰ͋Δ͜ͱʯΛදݱͰ͖Δ
    36
    

    View Slide

37. • Promise(Future) ύλʔϯ
    • PromiseK
    • Hydra
    • RxSwift
    • etc
    • async/await
    • comming soon in Swift 5.x!?
    • ͜ͷݴޠ࢓༷Λϕʔεʹ Future ܕΛߏஙՄೳ
    CPSΛશ໘తʹஔ͖͔͑Մೳ͔ͱ͍͏ͱ೉͍͕͠ɺ
    બ୒ࢶΛ஌ͬͨ͏͑ͰύλʔϯΛબͼ͍ͨ
    37
    

    View Slide

38. ݁࿦
    ɾਓؒ͸ϛεΛ͠·͢
    ɾϛεΛ͢Δલʹɺ
    ද໌ΛίϯύΠϥ͕෼͔ΔܗͰॻ͚ͳ͍͔
    ҙࣝ͠ͳ͕Βઃܭ͠·͠ΐ͏
    38
    

    View Slide

39. ͓·͚
    ͱͯ΋5෼Ͱ͸ޠΓ͖Εͳ͍࿩
    39
    

    View Slide

40. ʮද໌ʯʹ͍ͭͯͷิ଍
    • Ҿ਺ɾ໭Γ஋ͷܕ͚͕ͩද໌Ͱ͸ͳ͍ͱݴ͚ͬͨΕͲ…
    • assert ͚ͩͰͳ͘ɺSwiftͰݴ͑͹ generics ΍ conditional conformance΋ද໌ͷํ๏
    • ΂ͭʹɺίϯύΠϥղऍෆೳͳද໌͸ྑ͘ͳ͍…Θ͚Ͱ͸ͳ͍
    • දݱྗΛ্͛Δͱֶशίετɾෳࡶੑ͕ϖΠ͠ͳ͍͜ͱ΋ଟ͍ͷͰɺͦ͜͸όϥϯε
    • ͨͱ͑͹ɺڽͬͨprotocolͷwhere۟ɺৗਓʹཧղग़དྷΔ͔ͬͯݴΘΕΔͱݫ͍͠ΑͶ…
    ɹ
    40
    

    View Slide

41. ิ଍ͷิ଍
    ٯʹݴ͑͹ɺ
    ܖ໿ʹΑΔઃܭ͸
    ݴޠΛ໰Θͣద༻Մೳͳ֓೦Ͱ͢
    t_wada͞ΜʹΑΔ
    ͋͑ͯPHPΛϕʔεʹͨ͠εϥΠυ
    PHPer͡Όͳͯ͘΋ΦεεϝͰ͢
    https://speakerdeck.com/twada/php-
    conference-2016
    41
    

    View Slide

42. ʮܧଓ౉͠ʯʹ͍ͭͯͷิ଍
    • ࣮͸ async/await͸ʮ಺෦తͳCPSม׵ʯͦͷ΋ͷͱ͍͑·͢
    Continuation Passing Style Revisited
    – Fabulous Adventures In Coding
    https://blogs.msdn.microsoft.com/ericlippert/2010/10/21/
    continuation-passing-style-revisited-part-one/
    ͦͷ࿨༁
    matarillo.com: ܧଓ౉͠ελΠϧ(CPS)ͱඇಉظߏจ(async/await)
    https://matarillo.com/general/cps
    42
    

    View Slide

43. Swiftͷ async/await ͱ
    ܧଓͱ Future ͷؔ܎
    Chris Lattnerͷproposal2ʹΑΔͱɺ
    • ଞͷݴޠͰ͸ Future ͕·ͣ͋ͬͯɺͦͷ্ʹasync/await͕৐͔͍ͬͬͯΔ
    • Swiftͷasync/awaitͷઃܭͰ͸ͦΕΛલఏͱ͸ͤͣɺܧଓΛͦͷ··ѻ͏खஈΛ࿐ग़͍ͤͯ͞
    Δ
    • ͱ͸͍͑ Future ͱ͍͏ܕ෇͚͞Εͨঢ়ଶͰѻ͏ΠϯλϑΣʔε΋ߏஙՄೳͰ͢Αɺͱ͍͏͜ͱ
    2 https://gist.github.com/lattner/429b9070918248274f25b714dcfc7619
    yimajo͞Μͷʮasync/awaitݚڀಡຊʯ΋͋ΘͤͯͲ͏ͧ
    43
    

    View Slide

44. ؔ࿈ɿʮܖ໿ʹΑΔઃ
    ܭʯΛΩʔϫʔυͰ֦
    ு͢Δ࿩
    ʮܖ໿ʹΑΔઃܭʯʹ͍ͭͯৄղ͞Ε
    ͍ͯΔʮΦϒδΣΫτࢦ޲ೖ໳ʯʹ
    ͸ɺ
    ඇಉظʢฒߦʣॲཧΛ΋ͱʹ֦ுͨ͠
    ৔߹ͷܖ໿ͷϙϦγʔʹ͍ͭͯͷٞ࿦
    ΋͋Γ·͢
    ໘ന͍Αʂ
    44
    

    View Slide