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

2. None
3. None
4. None
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6. None

7. Q. Swi' ͰΤϥʔΛදͦ͏ͱࢥͬͨ ͱ͖ʹԿΛ࢖͍·͔͢ʁ

8. throw FooError()

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

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

11. fatalError()

12. assert(...)

13. precondition(...)

14. assertionFailure()

15. preconditionFailure()

16. fooOrNil!

17. array[-1]

18. Int.max + 1

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

20. func foo() { foo() }

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() }

22. Javaͷ৔߹ Throwable -+- Exception -+- RuntimeException -+- NullPointerException | |

    +- IndexOutOfBoundsException | | ... | | | +- IOException | +- SQLException | ... | +- Error - ... -+- OutOfMemoryError +- StackOverflowError ...

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() }
24. None
25. None
26. None
27. None
28. None

29. Simple domain errors Recoverable errors Universal errors Logic failures

30. Simple domain errors

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

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

    Optional Λฦ͢͜ͱͰද͢

33. let element: Int? = array.first

34. let value = dictionary["unknownKey"]

35. Recoverable errors

36. try fileManager .removeItem(at: url)

37. Recoverable errors • ༷ʑͳݪҼͰΦϖϨʔγϣϯ͕ࣦഊ͢Δ • ࣦഊͷݪҼΛ஌Γ͍ͨ • ݪҼผʹϋϯυϦϯά͍ͨ͠ • Swi%

    Ͱ͸ Error Λ throw ͢Δ͜ͱͰද͢

38. ճ෮ՄೳͳΤϥʔ Simple domain errors Recoverable errors

39. ճ෮ෆೳͳΤϥʔ Universal errors Logic failures

40. Universal errors

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

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") }

43. func foo() { foo() }

44. Ctrl + C

45. thread.cancel()

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

    fatalError ʣ

47. Logic failures

48. fooOrNil!

49. Int.max + 1

50. array[-1]

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 } } } }

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 } } } }

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 } } } }

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 } } } }

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 } } } }

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

57. ؔ਺ -Onone -O -Ounchecked fatalError ◦ ◦ ◦ precondi/on ◦

    ◦ assert ◦ ※ ◦͕෇͍͍ͯͳ͍૊Έ߹Θͤ͸νΣοΫ͕লུ͞ΕΔ

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 } } } }

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 } } } }

60. precondition ͩͱ͏Ε͍͠ཧ༝ // guard ͱ fatalError ͰΠϯσοΫεͷνΣοΫ struct Array<Element> {

    subscript(index: Int): Element { get { guard 0 <= index && index < count else { fatalError() } ... } set { ... } } }

61. precondition ͩͱ͏Ε͍͠ཧ༝ // guard ͱ fatalError ͰΠϯσοΫεͷνΣοΫ struct Array<Element> {

    subscript(index: Int): Element { get { guard 0 <= index && index < count else { fatalError() } ... } set { ... } } }

62. precondition ͩͱ͏Ε͍͠ཧ༝ // precondition ͸ -Ounchecked ͰऔΓআ͔ΕΔ struct Array<Element> {

    subscript(index: Int): Element { get { precondition(0 <= index && index < count) ... } set { ... } } }

63. -Onone ͷͱ͖ͷڍಈ // arrayindex.swift let a = [2, 3, 5]

    print(a[3]) $ swift arrayindex.swift fatal error: Index out of range

64. -Ounchecked ͷͱ͖ͷڍಈ // arrayindex.swift let a = [2, 3, 5]

    print(a[3]) $ swift -Ounchecked arrayindex.swift 2392130230941712

65. -Ounchecked ͷͱ͖ͷڍಈ let a: Int? = nil print(a!) // ࣮ߦ࣌ΤϥʔʹͳΒͳ͍

    let b: UInt8 = 255 print(b + 1) // ࣮ߦ࣌ΤϥʔʹͳΒͳ͍

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

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])

68. Simple domain errors Recoverable errors Universal errors Logic failures

69. ΤϥʔͷछྨͷܾΊํ ͲΜͳ಺༰ͷΤϥʔ͔ ͲͷΑ͏ʹΤϥʔϋϯυϦϯά͍͔ͤͨ͞

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") }

71. // Universal error Ͱ͸ͳ͘ Simple domain error Ͱ͋ͬͯ΄͍͠ guard let

    a = malloc(MemoryLayout<Int>.size * 100_000_000) else { showAlert("ϝϞϦ͕଍Γ·ͤΜɻ") return } // a Λ࢖͏ॲཧ

72. // Simple domain error → Logic failure let number: Int

    = Int(string)!

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

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 } } } }

75. ΫΠζλΠϜ

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

    ໰ - ඞͣࡾ୒ͷͲΕ͔ʹखΛڍ͛Δ

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

    ໰ - ඞͣࡾ୒ͷͲΕ͔ʹखΛڍ͛Δ

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

    ໰ - ඞͣࡾ୒ͷͲΕ͔ʹखΛڍ͛Δ

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

    ໰ - ඞͣࡾ୒ͷͲΕ͔ʹखΛڍ͛Δ

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

81. Q1. ϦόʔγͷϘʔυ

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

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 } ... } ... }

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() } ... } ... }

85. 3. Logic failure struct Board { subscript(x: Int, y: Int)

    -> Disk? { precondition((0..<8).contains(x)) precondition((0..<8).contains(y)) ... } ... }

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

    failure

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

    failure

88. | ◦◦◦•|

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91. | •◦◦◦ |

92. | ◦◦◦|

93. | •◦◦◦|

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 } ... } ... }

95. struct Board { subscript(x: Int, y: Int) -> Disk? {

    precondition((0..<8).contains(x)) precondition((0..<8).contains(y)) ... } ... }

96. Q2. ΞϓϦʹόϯυϧ͞Εͨσʔλ

97. let foo: Foo = loadFoo()

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) }

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() } }

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) }

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

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

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

     ... } // image Λ࢖͏ॲཧ

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

105. Q3. ηϯαʔ͔Βͷσʔλऔಘ

106. let foo: Foo = readFoo()

107. 1. Recoverable error func readFoo() throws -> Foo { guard

     isFooSensorAvailable() else { throw ... } ... }

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

     else { fatalError() } ... }

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

     }

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

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

112. Q4. ήʔϜͷηʔϒσʔλ

113. let game: Game? = loadGame()

114. 1. Recoverable error func loadGame() throws -> Game? { ...

     guard hash == savedHash else { throw ... } ... }

115. 2. Universal error func loadGame() -> Game? { ... guard

     hash == savedHash else { fatalError() } ... }

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

     == savedHash) ... }

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

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

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

120. None

121. // ϥΠϒϥϦϨΠϠʔ func loadGame() -> Game? { ... } //

     ΞϓϦϨΠϠʔ func ... { guard let game = loadGame() else { fatalError() } // game Λ࢖͏ίʔυ }

122. Q5. ը૾ͷੜ੒

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

124. 1. Simple domain error struct Image<Pixel> { 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 } ... } }

125. 2. Universal error struct Image<Pixel> { 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() } ... } }

126. 3. Logic failure struct Image<Pixel> { init(width: Int, height: Int,

     pixels: [Pixel]) { precondition(width >= 0) precondition(height >= 0) precondition(pixels.count == width) ... } }

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

     failure

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

     failure

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

     failure

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

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