構造的差分ライブラリ開発時の悲劇・喜劇

by Kuniwak

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ߏ଄తࠩ෼ϥΠϒϥϦ  ։ൃ࣌ͷ൵ܶتܶ σόοάΛॿ͚Δ

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ߏ଄తͳࠩ෼ͱ͸Կ͔ ·ͣ͸

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func testExample1() { let a = Example( key1: "I'm not changed", key2: "I'm deleted" ) let b = Example( key1: "I'm not changed", key2: "I'm inserted" ) XCTAssertEqual(a, b) } Α͋͘ΔTUSVDUͷൺֱ

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XCTAssertEqual failed: ("Example(key1: "I\'m not changed", key2: "I\'m deleted")") is not equal to ("Example(key1: "I\'m not changed", key2: "I\'m inserted")") - ςετ݁Ռ͸ඇৗʹΘ͔ΓͮΒ͍

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IUUQHJUIVCDPN,VOJXBL.JSSPS%J⒎,JU ͦ͜Ͱ

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import MirrorDiffKit func testExample2() { let a = Example( key1: "I'm not changed", key2: "I'm deleted" ) let b = Example( key1: "I'm not changed", key2: "I'm inserted" ) XCTAssertEqual(a, b, diff(between: a, and: b)) } ࣦഊ࣌ͷϝοηʔδʹ  .JSSPS%J⒎,JUͷEJ⒎Λࢦఆ .JSSPS%J⒎,JUΛJNQPSU

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struct Example { key1: "I'm not changed" - key2: "I'm deleted" + key2: "I'm inserted" } ͜Ε͕ߏ଄తͳࠩ෼ ͙͢ʹࠩҟ͕Θ͔Γ·͢

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[ "I'm not changed" "I'm not changed" - "I'm deleted" "I'm not changed" + "I'm inserted" ] ഑ྻͷॱংมߋͳͲ΋  ߏ଄తͳࠩ෼Ͱ͢ ͜Ε΋ݟ΍͘͢දࣔ͞Ε·͢

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IUUQHJUIVCDPN,VOJXBL.JSSPS%J⒎,JU ΑΖ͓͘͠ئ͍͠·͢

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࢓૊Έͷղઆ ࠩ෼ܭࢉͷ

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let example = Example( key1: "I'm not changed", key2: "I'm deleted" ) let hint = ( subject: Example.self, displayStyle: .struct, children: [ (label: "key1", value: "I'm not changed"), (label: "key2", value: "I'm deleted"), ] ) ߏ଄తͳࠩ෼ͷܭࢉʹ͸ɺ  ࣍ͷΑ͏ͳΦϒδΣΫτͷ  ߏ଄ͷώϯτ͕ෆՄܽͰ͢ ΦϒδΣΫτͷܕ ΦϒδΣΫτͷछྨ ϓϩύςΟͷ໊લͱ஋

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ͦͷػೳΛ୲͏ͷ͕.JSSPS  ʢඪ४ϥΠϒϥϦͷ"1*Ͱ͢ʣ

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let example = Example( key1: "I'm not changed", key2: "I'm deleted" ) let mirror = Mirror(reflecting: example) let hint = ( subject: mirror.subjectType, displayStyle: mirror.displayStyle, children: mirror.children ) ௐ΂͍ͨΦϒδΣΫτ͔Β  .JSSPSΦϒδΣΫτΛ  ࡞੒͢Δͱɺ ܕ৘ใ΍ΦϒδΣΫτͷछྨɺ  ϓϩύςΟͷ໊લͱ஋ͳͲΛ  ೖखͰ͖·͢

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.JSSPS%J⒎,JU͸ɺ  ͜ͷ.JSSPSΛ࢖ͬͯ  ࣮ݱ͞Ε͍ͯ·͢

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͍ΖΜͳ͜ͱ͕Ͱ͖ͦ͏Ͱ  ເͷ޿͕Δ"1*Ͱ͢Ͷ

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تܶ͸͜͜·Ͱͩ

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΍͹͍OJM͕΍͹͍໰୊ ൵ܶͦͷ

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struct Example { let any: Any? } let example = Example(any: nil) if let first = Mirror(reflecting: example) .children.first { print(first.value) } ϓϩύςΟΛOJMͰॳظԽ ϓϩύςΟͷ஋ΛݟΔͱɺ  ઌ΄ͲOJMͰॳظԽͨ͠ͷͰ  OJMʹͳ͍ͬͯΔ "OZ ͷϓϩύςΟ͕͋ΔTUSVDU .JSSPSΛ࡞੒ͯ͠ɺTUSVDUͷ  ϓϩύςΟͷώϯτΛೖख

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struct Example { let any: Any? } let example = Example(any: nil) if let first = Mirror(reflecting: example) .children.first { print(first.value == nil) print(first.value) } GBMTF OJMͰ΋͔֬ΊͯΈΑ͏ ͔͠͠ೖ͍ͬͯΔͷ͸OJMʜ

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ߟ࡯ฤ ൵͠Έͷ

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"OZʹ͸  ͳΜͰ΋ೖΔ ᶃ Int String Bool Any

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0QUJPOBM΋  ೖΕΒΕΔ ᶄ Optional Any

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͢ΔͱOJM΋  ೖΓ͏Δ ᶄ nil Any

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ᶄ nil Any == nil GBMTF

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let x: Any? = nil let wrapper: Any = x // WARNING: Comparing non-optional value of // type 'Any' to nil always returns false print(x == nil) ࣮͸ղઆͨ͠ྫΛίʔυʹ͢Δͱܯࠂ͕ग़Δ ʮ0QUJPOBM͡Όͳ͍஋ͱOJMΛ  ɹൺֱͯ͠΋ৗʹGBMTFͩΑʯ

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ͭ·Γɺ"OZʹOJMΛ  ೖΕͯ͸ͳΒͳ͍ͷͰ͢

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͔͠͠ɺ.JSSPSͰऔಘͨ͠  ϓϩύςΟͷ஋ͷܕ͸  ໰౴ແ༻Ͱ"OZͱ͍͏൵͠Έ ͳͷͰɺϓϩύςΟʹOJMΛ΋ͭ  ΦϒδΣΫτΛ.JSSPSʹ͔͚Δͱ  Ϋϥογϡͷةݥ͕͋Γ·͢

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.JSSPS%J⒎,JUͰ͸͜ͷ໰୊ʹ  ରॲ͍ͯ͠·͢ͷͰ҆͝৺Λʜ

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ཁૉ਺ͷUVQMF໰୊ ൵ܶͦͷ

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enum Example { case zero case one(key: String) case two(key1: String, key2: String) } 4XJGUͰ͸FOVNͷDBTFʹ෇ଐ͢Δ஋ΛఆٛͰ͖·͢ ͜ͷ෇ଐ͢Δ஋͸BTTPDJBUFEWBMVFTͱݺ͹Ε͍ͯ·͢

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enum Example { case one(key: String) case two(key1: String, key2: String) } func test() { let x1: Example = .one(key: "value") let x2: Example = .two(key1: "value1", key2: "value2") let mirror1 = Mirror(reflecting: x1) let mirror2 = Mirror(reflecting: x2) dump(mirror1.children.first!.value) dump(mirror2.children.first!.value) } ͦΕͧΕΛ.JSSPSʹ͔͚·͢ ͜͜Ͱ͸BTTPDJBUFEWBMVFTͷ  ཁૉ਺͕ҟͳΔͭͷDBTFΛ  ఆٛ͠·͢ BTTPDJBUFWBMVFT͸ɺ  TUSVDUͷϓϩύςΟͱ  ಉ͡Α͏ʹDIJMESFOͰ  දݱ͞Ε·͢ ͦΕͧΕͷDIJMESFOΛ  ֬ೝͯ͠Έ·͠ΐ͏

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enum Example { case one(key: String) case two(key1: String, key2: String) } func test() { let x1: Example = .one(key: "value") let x2: Example = .two(key1: "value1", key2: "value2") let mirror1 = Mirror(reflecting: x1) let mirror2 = Mirror(reflecting: x2) dump(mirror1.children.first!.value) dump(mirror2.children.first!.value) } BTTPDJBUFEWBMVFT͕  ͭͷ৔߹ WBMVF ͭͷ৔߹    LFZWBMVF   LFZWBMVF  ܕ͕ҧ͏

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ߟ࡯ฤ ൵͠Έͷ

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let y: Any = (number: 123) print(type(of: y)) ܕΛௐ΂ͯΈΔͱ  *OU ຊ౰͸BTTPDJBUFEWBMVFTͷཁૉ਺͕  ͍ͭ͘Ͱ͋ΕɺDIJMESFOͷܕ͸UVQMFʹ  ͔ͨͬͨ͠ͷͰ͸ͱਪଌ ͔͠͠ɺཁૉ਺ͷ͚࣌ͩࣄ৘͕͋ͬͯ  UVQMFʹͰ͖ͳ͔͔ͬͨ΋͠Εͳ͍ͷͰɺ  ࢼ͠ʹཁૉ͕ͭͷUVQMFΛ࡞੒ͯ͠ΈΔ UVQMFͰ͸ͳ͍

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// Error: cannot create a single-element tuple with // an element label let x: (number: Int) = (number: 123)    let y: Any = (number: 123) print(type(of: y)) // Int ࣮͸ɺ4XJGUͷܕͰ͸ཁૉ͕ͭͷUVQMF͸ఆٛͰ͖ͳ͍ ͔͠͠ɺཁૉ਺ͷUVQMFܕ͕  ࡞Εͳ͍͚ͩͳͷͰɺܕΛ  "OZʹͯ͠͠·͑͹ཁૉ਺ͷ  UVQMFΒ͖͠΋ͷΛఆٛͰ͖Δ ͔͠͠ɺఆٛͰ͖ͨͱͯ͠΋ɺ  ͦͷܕ͸ཁૉͷத਎ͷܕʹ  ͳΔΑ͏ͩ ͭ·Γɺཁૉ਺ͷUVQMF͸  ଘࡏͰ͖ͳ͍͜ͱ͕Θ͔Δ

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ཁૉ਺ͷUVQMFܕ͸ଘࡏͰ͖ͳ͍ͷͰɺ  ຊདྷ͸UVQMFͰ͋Δ͸ͣͷ  BTTPDJBUFEWBMVFT͕ɺཁૉ਺ͷ  ͱ͖ʹத਎͚ͩʹͳΔͷͰͨ͠ʜ

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.JSSPS%J⒎,JUͰ͸͜ͷ໰୊ʹ  ରॲ͍ͯ͠·͢ͷͰ҆͝৺Λʜ

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ΧδϡΞϧʹյΕΔ ൵ܶͦͷ

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·ͱΊ w .JSSPSͱ͍͏TUSVDUͳͲͷߏ଄Λ  ௐ΂ΔͨΊͷ"1*͕͋Γ·͢ w ৭ʑͰ͖ͦ͏Ͱເ͕޿͕Γ·͢ w ͔͠͠ɺ͔ͳΓͷͭΒΈ͕͋Γ·͢ͷͰ  ΍͍ͬͯ͘ࡍʹ͸.JSSPS%J⒎,JUͷ  ճආྫΛࢀߟʹ͢ΔͱΑ͍Ͱ͠ΐ͏