具体例とクイズで学ぶ、Swiftの4種類のエラーの使い分け

Transcript

1. ۩ମྫͱΫΠζͰֶͿɺ
   Swi$ͷ4छྨͷΤϥʔͷ࢖͍෼͚
   Yuta Koshizawa @koher
   

   View Slide

2. View Slide

3. View Slide

4. View Slide

5. View Slide

6. View Slide

7. Q. Swi' ͰΤϥʔΛදͦ͏ͱࢥͬͨ
   ͱ͖ʹԿΛ࢖͍·͔͢ʁ
   

   View Slide

8. throw FooError()
   

   View Slide

9. let number: Int? =
   Int(string)
   

   View Slide

10. let foo: Foo? = try? foo()
    

    View Slide

11. fatalError()
    

    View Slide

12. assert(...)
    

    View Slide

13. precondition(...)
    

    View Slide

14. assertionFailure()
    

    View Slide

15. preconditionFailure()
    

    View Slide

16. fooOrNil!
    

    View Slide

17. array[-1]
    

    View Slide

18. Int.max + 1
    

    View Slide

19. [Int](repeating: 42,
    count: Int.max)
    

    View Slide

20. func foo() { foo() }
    

    View Slide

21. throw FooError()
    let number: Int? = Int(String)
    let foo: Foo? = try? foo()
    fatalError()
    assert(...)
    assertionFailure()
    precondition(...)
    preconditionFailure()
    fooOrNil!
    array[-1]
    Int.max + 1
    [Int](repeating: 42, count: Int.max)
    func foo() { foo() }
    

    View Slide

22. Javaͷ৔߹
    Throwable -+- Exception -+- RuntimeException -+- NullPointerException
    | | +- IndexOutOfBoundsException
    | | ...
    | |
    | +- IOException
    | +- SQLException
    | ...
    |
    +- Error - ... -+- OutOfMemoryError
    +- StackOverflowError
    ...
    

    View Slide

23. throw FooError()
    let number: Int? = Int(string)
    let foo: Foo? = try? foo()
    fatalError()
    assert(...)
    assertionFailure()
    precondition(...)
    preconditionFailure()
    fooOrNil!
    array[-1]
    Int.max + 1
    [Int](repeating: 42, count: Int.max)
    func foo() { foo() }
    

    View Slide

24. View Slide

25. View Slide

26. View Slide

27. View Slide

28. View Slide

29. Simple domain errors
    Recoverable errors
    Universal errors
    Logic failures
    

    View Slide

30. Simple domain errors
    

    View Slide

31. let number: Int? =
    Int(string)
    

    View Slide

32. Simple domain errors
    • ΦϖϨʔγϣϯ͕ࣦഊ͢Δલఏ৚͕݅໌֬
    • ੒ޭ͔ࣦͨ͠ഊ͔͕ͨ͠෼͔Ε͹े෼
    • Swi% Ͱ͸ Optional Λฦ͢͜ͱͰද͢
    

    View Slide

33. let element: Int? =
    array.first
    

    View Slide

34. let value =
    dictionary["unknownKey"]
    

    View Slide

35. Recoverable errors
    

    View Slide

36. try fileManager
    .removeItem(at: url)
    

    View Slide

37. Recoverable errors
    • ༷ʑͳݪҼͰΦϖϨʔγϣϯ͕ࣦഊ͢Δ
    • ࣦഊͷݪҼΛ஌Γ͍ͨ
    • ݪҼผʹϋϯυϦϯά͍ͨ͠
    • Swi% Ͱ͸ Error Λ throw ͢Δ͜ͱͰද͢
    

    View Slide

38. ճ෮ՄೳͳΤϥʔ
    Simple domain errors
    Recoverable errors
    

    View Slide

39. ճ෮ෆೳͳΤϥʔ
    Universal errors
    Logic failures
    

    View Slide

40. Universal errors
    

    View Slide

41. [Int](repeating: 42,
    count: Int.max)
    

    View Slide

42. Universal error ͕ϋϯυϦϯάՄೳͩͬͨͱ͢Δͱ
    // ϝϞϦෆ଍ͷϋϯυϦϯάͷྫ
    let foo: Foo? = allocate(size(of: Foo))
    guard let foo = foo else {
    // Τϥʔϝοηʔδͷੜ੒Ͱ͞ΒʹϝϞϦෆ଍͕ى͜Δ͔΋
    showAlert("ϝϞϦ͕଍Γ·ͤΜɻ")
    }
    

    View Slide

43. func foo() { foo() }
    

    View Slide

44. Ctrl + C
    

    View Slide

45. thread.cancel()
    

    View Slide

46. Universal errors
    • ίʔυதͷࢸΔͱ͜ΖͰൃੜ͢Δ΋ͷ͕ଟ͍
    • ϋϯυϦϯά͠Α͏͕ͳ͍
    • ίʔυ͔Βൃੜͤ͞Δʹ͸ NSException ʢ·ͨ͸
    fatalError ʣ
    

    View Slide

47. Logic failures
    

    View Slide

48. fooOrNil!
    

    View Slide

49. Int.max + 1
    

    View Slide

50. array[-1]
    

    View Slide

51. Array ͷ subscript ͷࣦഊ͕ Logic failure ͳཧ༝
    // [Int] Λιʔτ͢Δؔ਺
    func sort(_ ns: inout [Int]) {
    for i in 0 ..< ns.count {
    for j in i + 1 ..< ns.count {
    if ns[j] < ns[i] {
    let t = ns[j]
    ns[j] = ns[i]
    ns[i] = t
    }
    }
    }
    }
    

    View Slide

52. Array ͷ subscript ͷࣦഊ͕ Logic failure ͳཧ༝
    // [Int] Λιʔτ͢Δؔ਺
    func sort(_ ns: inout [Int]) {
    for i in 0 ..< ns.count {
    for j in i + 1 ..< ns.count {
    if ns[j] < ns[i] {
    let t = ns[j]
    ns[j] = ns[i]
    ns[i] = t
    }
    }
    }
    }
    

    View Slide

53. Array ͷ subscript ͷࣦഊ͕ Logic failure ͳཧ༝
    // ..< Λ ... ʹͯ͠͠·͏ͱΠϯσοΫε͕͸Έग़ͯΤϥʔ
    func sort(_ ns: inout [Int]) {
    for i in 0 ... ns.count {
    for j in i + 1 ... ns.count {
    if ns[j] < ns[i] {
    let t = ns[j]
    ns[j] = ns[i]
    ns[i] = t
    }
    }
    }
    }
    

    View Slide

54. Array ͷ subscript ͷࣦഊ͕ Logic failure ͳཧ༝
    // Ͱ΋ɺ͜͜Ͱ nil ͕ฦ͖ͬͯͯ΋ϋϯυϦϯά͠Α͏͕ͳ͍
    func sort(_ ns: inout [Int]) {
    for i in 0 ... ns.count {
    for j in i + 1 ... ns.count {
    if ns[j] < ns[i] {
    let t = ns[j]
    ns[j] = ns[i]
    ns[i] = t
    }
    }
    }
    }
    

    View Slide

55. Array ͷ subscript ͷࣦഊ͕ Logic failure ͳཧ༝
    // Ͳ͏ͤ ! ͢Δ͜ͱʹͳͬͯແବ
    func sort(_ ns: inout [Int]) {
    for i in 0 ... ns.count {
    for j in i + 1 ... ns.count {
    if ns[j]! < ns[i]! {
    let t = ns[j]!
    ns[j] = ns[i]!
    ns[i] = t
    }
    }
    }
    }
    

    View Slide

56. Logic failures
    • ίʔυͷϛεʹΑͬͯൃੜ
    • ࣮ߦ࣌Ͱ͸ͳ͘ίʔυͷमਖ਼ʹΑͬͯରԠ
    • precondition, assert ͳͲͰൃੜͤ͞Δ
    

    View Slide

57. ؔ਺ -Onone -O -Ounchecked
    fatalError ○ ○ ○
    precondi/on ○ ○
    assert ○
    ※ ○͕෇͍͍ͯͳ͍૊Έ߹Θͤ͸νΣοΫ͕লུ͞ΕΔ
    

    View Slide

58. precondition ͩͱ͏Ε͍͠ཧ༝
    // [Int] Λιʔτ͢Δؔ਺
    func sort(_ ns: inout [Int]) {
    for i in 0 ..< ns.count {
    for j in i + 1 ..< ns.count {
    if ns[j] < ns[i] {
    let t = ns[j]
    ns[j] = ns[i]
    ns[i] = t
    }
    }
    }
    }
    

    View Slide

59. precondition ͩͱ͏Ε͍͠ཧ༝
    // [Int] Λιʔτ͢Δؔ਺
    func sort(_ ns: inout [Int]) {
    for i in 0 ..< ns.count {
    for j in i + 1 ..< ns.count {
    if ns[j] < ns[i] {
    let t = ns[j]
    ns[j] = ns[i]
    ns[i] = t
    }
    }
    }
    }
    

    View Slide

60. precondition ͩͱ͏Ε͍͠ཧ༝
    // guard ͱ fatalError ͰΠϯσοΫεͷνΣοΫ
    struct Array {
    subscript(index: Int): Element {
    get {
    guard 0 <= index && index < count else {
    fatalError()
    }
    ...
    }
    set { ... }
    }
    }
    

    View Slide

61. precondition ͩͱ͏Ε͍͠ཧ༝
    // guard ͱ fatalError ͰΠϯσοΫεͷνΣοΫ
    struct Array {
    subscript(index: Int): Element {
    get {
    guard 0 <= index && index < count else {
    fatalError()
    }
    ...
    }
    set { ... }
    }
    }
    

    View Slide

62. precondition ͩͱ͏Ε͍͠ཧ༝
    // precondition ͸ -Ounchecked ͰऔΓআ͔ΕΔ
    struct Array {
    subscript(index: Int): Element {
    get {
    precondition(0 <= index && index < count)
    ...
    }
    set { ... }
    }
    }
    

    View Slide

63. -Onone ͷͱ͖ͷڍಈ
    // arrayindex.swift
    let a = [2, 3, 5]
    print(a[3])
    $ swift arrayindex.swift
    fatal error: Index out of range
    

    View Slide

64. -Ounchecked ͷͱ͖ͷڍಈ
    // arrayindex.swift
    let a = [2, 3, 5]
    print(a[3])
    $ swift -Ounchecked arrayindex.swift
    2392130230941712
    

    View Slide

65. -Ounchecked ͷͱ͖ͷڍಈ
    let a: Int? = nil
    print(a!) // ࣮ߦ࣌ΤϥʔʹͳΒͳ͍
    let b: UInt8 = 255
    print(b + 1) // ࣮ߦ࣌ΤϥʔʹͳΒͳ͍
    

    View Slide

66. Logic failure ͸ίʔυͷϛεͷΑͬ
    ͯҾ͖ى͜͞ΕΔ
    ↕
    ίʔυͷϛε͕ͳ͚Ε͹ Logic
    failure ͸ى͜Βͳ͍
    

    View Slide

67. assert ͷ࢖༻ྫ
    assert ͸಺෦తͳ੔߹ੑͷνΣοΫʹ࢖͏
    import TensorSwift
    // 10000 ਓ෼ͷ྆खͷࢦͷ௕͞
    let tensor = Tensor(shape: [10000, 2, 5], elements: ...)
    // [ਓ, ࠨӈ, ࢦ] ͔Β [ࢦ, ਓ, ࠨӈ] ʹม׵
    let transposed = tensor.transposed([2, 0, 1])
    // ࠨखͷσʔλ͚ͩΛऔΓग़͢
    let lefthand = tensor[..., ..., 1]
    // [ࢦ, ਓ] ͷॱʹͳ͍ͬͯͯ΄͍͚͠Ͳॲཧ͕ෳࡶͰࣗ৴͕࣋ͯͳ͍ͷͰνΣοΫ
    assert(lefthand.shape == [5, 10000])
    

    View Slide

68. Simple domain errors
    Recoverable errors
    Universal errors
    Logic failures
    

    View Slide

69. ΤϥʔͷछྨͷܾΊํ
    ͲΜͳ಺༰ͷΤϥʔ͔
    ͲͷΑ͏ʹΤϥʔϋϯυϦϯά͍͔ͤͨ͞
    

    View Slide

70. // Simple domain error Ͱͳ͘ Recoverable Ͱ͋ͬͯ΄͍͠
    let string = "99999999999999999999999999"
    ...
    do {
    let number: Int = try Int(string)
    } catch is OverflowError {
    showAlert("\(Int.min) - \(Int.max) ͷ஋Λೖྗͯ͠Լ͍͞ɻ")
    } catch {
    showAlert("੔਺Λೖྗͯ͠Լ͍͞ɻ")
    }
    

    View Slide

71. // Universal error Ͱ͸ͳ͘ Simple domain error Ͱ͋ͬͯ΄͍͠
    guard let a = malloc(MemoryLayout.size * 100_000_000) else {
    showAlert("ϝϞϦ͕଍Γ·ͤΜɻ")
    return
    }
    // a Λ࢖͏ॲཧ
    

    View Slide

72. // Simple domain error → Logic failure
    let number: Int = Int(string)!
    

    View Slide

73. from \ to SDE RE UE LF
    SDE - guard let
    throw
    guard let
    fatalError
    !
    RE try? - do-catch
    fatalError
    try!
    UE -
    LF if/guard
    return nil
    if/guard
    throw
    if/guard
    fatalError
    -
    SDE: Simple domain error, RE: Recoverable error,
    UE: Universal error, LF: Logic failure
    

    View Slide

74. // Ͳ͏ͤ ! ͢Δ͜ͱʹͳͬͯແବ
    func sort(_ ns: inout [Int]) {
    for i in 0 ... ns.count {
    for j in i + 1 ... ns.count {
    if ns[j]! < ns[i]! {
    let t = ns[j]!
    ns[j] = ns[i]!
    ns[i] = t
    }
    }
    }
    }
    

    View Slide

75. ΫΠζλΠϜ
    

    View Slide

76. ΫΠζͷϧʔϧ
    - ࡾ୒ܗࣜ
    - ੍ݶ࣌ؒ͸ 30 ඵ
    - શ෦Ͱ 5 ໰
    - ඞͣࡾ୒ͷͲΕ͔ʹखΛڍ͛Δ
    

    View Slide

77. ΫΠζͷϧʔϧ
    - ࡾ୒ܗࣜ
    - ੍ݶ࣌ؒ͸ 30 ඵ
    - શ෦Ͱ 5 ໰
    - ඞͣࡾ୒ͷͲΕ͔ʹखΛڍ͛Δ
    

    View Slide

78. ΫΠζͷϧʔϧ
    - ࡾ୒ܗࣜ
    - ੍ݶ࣌ؒ͸ 30 ඵ
    - શ෦Ͱ 5 ໰
    - ඞͣࡾ୒ͷͲΕ͔ʹखΛڍ͛Δ
    

    View Slide

79. ΫΠζͷϧʔϧ
    - ࡾ୒ܗࣜ
    - ੍ݶ࣌ؒ͸ 30 ඵ
    - શ෦Ͱ 5 ໰
    - ඞͣࡾ୒ͷͲΕ͔ʹखΛڍ͛Δ
    

    View Slide

80. @koher
    h"ps:/
    /twi"er.com/koher
    

    View Slide

81. Q1. ϦόʔγͷϘʔυ
    

    View Slide

82. let disk: Disk?
    = board[x, y]
    

    View Slide

83. 1. Simple domain error
    struct Board {
    subscript(x: Int, y: Int) -> Disk? {
    guard (0..<8).contains(x) else { return nil }
    guard (0..<8).contains(y) else { return nil }
    ...
    }
    ...
    }
    

    View Slide

84. 2. Universal error
    struct Board {
    subscript(x: Int, y: Int) -> Disk? {
    guard (0..<8).contains(x) else { fatalError() }
    guard (0..<8).contains(y) else { fatalError() }
    ...
    }
    ...
    }
    

    View Slide

85. 3. Logic failure
    struct Board {
    subscript(x: Int, y: Int) -> Disk? {
    precondition((0..<8).contains(x))
    precondition((0..<8).contains(y))
    ...
    }
    ...
    }
    

    View Slide

86. γϯΩϯάλΠϜ
    1. Simple domain error
    2. Universal error
    3. Logic failure
    

    View Slide

87. ౴͑
    1. Simple domain error
    2. Universal error
    3. Logic failure
    

    View Slide

88. | ○○○●|
    

    View Slide

89. | ●○○○●|
    

    View Slide

90. | ○○○ |
    

    View Slide

91. | ●○○○ |
    

    View Slide

92. | ○○○|
    

    View Slide

93. | ●○○○|
    

    View Slide

94. struct Board {
    subscript(x: Int, y: Int) -> Disk? {
    guard (0..<8).contains(x) else { return nil }
    guard (0..<8).contains(y) else { return nil }
    ...
    }
    ...
    }
    

    View Slide

95. struct Board {
    subscript(x: Int, y: Int) -> Disk? {
    precondition((0..<8).contains(x))
    precondition((0..<8).contains(y))
    ...
    }
    ...
    }
    

    View Slide

96. Q2. ΞϓϦʹόϯυϧ͞Εͨσʔλ
    

    View Slide

97. let foo: Foo = loadFoo()
    

    View Slide

98. 1. Recoverable error
    func loadFoo() throws -> Foo {
    guard let path = Bundle.main.path(forResource: "Foo", ofType: "json") else {
    throw ...
    }
    let url = URL(fileURLWithPath: path)
    let data = try Data(contentsOf: url)
    return try JSONDecoder().decode(Foo.self, from: data)
    }
    

    View Slide

99. 2. Universal error
    func loadFoo() -> Foo {
    guard let path = Bundle.main.path(forResource: "Foo", ofType: "json") else {
    fatalError()
    }
    let url = URL(fileURLWithPath: path)
    do {
    let data = try Data(contentsOf: url)
    return try JSONDecoder().decode(Foo.self, from: data)
    } catch {
    fatalError()
    }
    }
    

    View Slide

100. 3. Logic failure
     func loadFoo() -> Foo {
     let path = Bundle.main.path(forResource: "Foo", ofType: "json")!
     let url = URL(fileURLWithPath: path)
     let data = try! Data(contentsOf: url)
     return try! JSONDecoder().decode(Foo.self, from: data)
     }
     

     View Slide

101. γϯΩϯάλΠϜ
     1. Recoverable error
     2. Universal error
     3. Logic failure
     

     View Slide

102. ౴͑
     1. Recoverable error
     2. Universal error
     3. Logic failure
     

     View Slide

103. guard let image = UIImage(named: "Foo") else {
     // ΤϥʔϋϯυϦϯά
     ...
     }
     // image Λ࢖͏ॲཧ
     

     View Slide

104. let image = UIImage(named: "Foo")!
     // image Λ࢖͏ॲཧ
     

     View Slide

105. Q3. ηϯαʔ͔Βͷσʔλऔಘ
     

     View Slide

106. let foo: Foo = readFoo()
     

     View Slide

107. 1. Recoverable error
     func readFoo() throws -> Foo {
     guard isFooSensorAvailable() else {
     throw ...
     }
     ...
     }
     

     View Slide

108. 2. Universal error
     func readFoo() -> Foo {
     guard isFooSensorAvailable() else {
     fatalError()
     }
     ...
     }
     

     View Slide

109. 3. Logic failure
     func readFoo() -> Foo {
     precondition(isFooSensorAvailable())
     ...
     }
     

     View Slide

110. γϯΩϯάλΠϜ
     1. Recoverable error
     2. Universal error
     3. Logic failure
     

     View Slide

111. ౴͑
     1. Recoverable error
     2. Universal error
     3. Logic failure
     

     View Slide

112. Q4. ήʔϜͷηʔϒσʔλ
     

     View Slide

113. let game: Game? =
     loadGame()
     

     View Slide

114. 1. Recoverable error
     func loadGame() throws -> Game? {
     ...
     guard hash == savedHash else {
     throw ...
     }
     ...
     }
     

     View Slide

115. 2. Universal error
     func loadGame() -> Game? {
     ...
     guard hash == savedHash else {
     fatalError()
     }
     ...
     }
     

     View Slide

116. 3. Logic failure
     func loadGame() -> Game? {
     ...
     precondition(hash == savedHash)
     ...
     }
     

     View Slide

117. γϯΩϯάλΠϜ
     1. Recoverable error
     2. Universal error
     3. Logic failure
     

     View Slide

118. ౴͑
     1. Recoverable error
     2. Universal error
     3. Logic failure
     

     View Slide

119. ౴͑
     1. Recoverable error
     2. Universal error
     3. Logic failure
     

     View Slide

120. View Slide

121. // ϥΠϒϥϦϨΠϠʔ
     func loadGame() -> Game? {
     ...
     }
     // ΞϓϦϨΠϠʔ
     func ... {
     guard let game = loadGame() else {
     fatalError()
     }
     // game Λ࢖͏ίʔυ
     }
     

     View Slide

122. Q5. ը૾ͷੜ੒
     

     View Slide

123. let image = Image(
     width: width,
     height: height,
     pixels: pixels)
     

     View Slide

124. 1. Simple domain error
     struct Image {
     init?(width: Int, height: Int, pixels: [Pixel]) {
     guard width >= 0 else { return nil }
     guard height >= 0 else { return nil }
     guard pixels.count == width * height else { return nil }
     ...
     }
     }
     

     View Slide

125. 2. Universal error
     struct Image {
     init(width: Int, height: Int, pixels: [Pixel]) {
     guard width >= 0 else { return fatalError() }
     guard height >= 0 else { return fatalError() }
     guard pixels.count == width * height else { return fatalError() }
     ...
     }
     }
     

     View Slide

126. 3. Logic failure
     struct Image {
     init(width: Int, height: Int, pixels: [Pixel]) {
     precondition(width >= 0)
     precondition(height >= 0)
     precondition(pixels.count == width)
     ...
     }
     }
     

     View Slide

127. γϯΩϯάλΠϜ
     1. Simple domain error
     2. Universal error
     3. Logic failure
     

     View Slide

128. ౴͑
     1. Simple domain error
     2. Universal error
     3. Logic failure
     

     View Slide

129. ౴͑
     1. Simple domain error
     2. Universal error
     3. Logic failure
     

     View Slide

130. let a = [2, 3, 5]
     a.prefix(-1) // Logic failure
     

     View Slide

131. print(3...2) // Logic failure
     

     View Slide