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
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() }
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
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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
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