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Tomoki Ota ʲGoݴޠʳ ΤϥʔϋϯυϦϯά

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ύχοΫ Τϥʔ Τϥʔϥοϐϯά Τϥʔͷൺֱ(error.As(), error.Is()) ΤϥʔͷϥΠϒϥϦ μϒϧϋϯυϦϯά ͓·͚ ΞδΣϯμ 2

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panic

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Goʹ͓͚Δྫ֎ॲཧ 4 ྫ֎ : ҙਤ͠ͳ͍Τϥʔ → Ͱ͖Δ͚ͩগͳ͍ํ͕͍͍

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Goʹ͓͚Δྫ֎ॲཧ 5 •errorܕΛฦ͢ˡਪ঑ •panic/recoverΛར༻͢Δ

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panic 6

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recover 7

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recover 8

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panicͤ͞Δ΂͖ͱ͖ 9 •७ਮͳϓϩάϥϚʔΤϥʔ •ΞϓϦέʔγϣϯ͕ඞਢґଘؔ܎Λඞཁͱ͢Δʹ΋ؔΘΒͣ ॳظԽʹࣦഊ͢Δͱ͖

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७ਮͳϓϩάϥϚʔΤϥʔ 10 net/httpύοέʔδͷWriteHeader εςʔλείʔυ͕༗ޮԽͲ͏͔Λݕࠪ͢ΔͨΊʹcheckWriteHeaderCode()ΛݺͿ

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ΞϓϦέʔγϣϯ͕ඞਢͷґଘؔ܎ͷ࡞੒ʹࣦഊ͢Δͱ͖ 11 regexpύοέʔδʹ͸ɺจࣈྻ͔Βਖ਼نදݱΛ࡞੒͢Δؔ਺ͱͯ͠ɺҎԼͷ͕̎ͭ͋Δɻ •Compile : *regexp.RegexpͱΤϥʔΛฦ͢ •MustCompile : Τϥʔ͕ൃੜͨ͠ΒύχοΫΛൃੜͤ͞Δ

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Τϥʔ

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ΤϥʔϋϯυϦϯάͱ͸ʁ 13 ϓϩάϥϛϯάͰ͸ࣦഊ͕ى͜ΓಘΔؔ਺Λݺͼग़͢ͱ ඞͣʮΤϥʔʯΛऔΓѻ͏ඞཁ͕͋Δɻ

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ΤϥʔϋϯυϦϯάͱ͸ʁ 14 ى͖ͨΤϥʔʹରͯ͠ͲͷΑ͏ͳ࣮૷Λߦ͏΂͖͔ͷऔΓܾΊ΍ઃܭ

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ΤϥʔϋϯυϦϯάͱ͸ʁ •ϑΝΠϧ͕ଘࡏ͠ͳ͍ •ΞΫηεݖݶ͕ͳ͍ •σΟεΫ͕յΕ͍ͯΔ •ׂΓࠐΈͷൃੜ •ڧ੍ऴྃ͢Δ •ϦτϥΠ͢Δ •৽͘͠ϑΝΠϧΛ࡞੒͢Δ •ϩάΛग़ྗ͢Δ •ݺͼग़͠ݩʹ஌ΒͤΔ ϑΝΠϧΛ։࣌͘ͷ I/OΤϥʔ Τϥʔॲཧ

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Τϥʔͱ͸ʁ 16

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Τϥʔͱ͸ʁ 17 ϓϩάϥϜ : ਖ਼ৗ࣌ͱҟৗ࣌ͱ͍͏2ͭͷঢ়ଶΛ࣋ͭ Τϥʔ : ҟৗͱ͍͏ঢ়ଶΛϓϩάϥϚʔʹ஌ΒͤΔͨΊͷํ๏

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ଟݴޠʹ͓͚ΔΤϥʔ 18 Java΍RubyɺPythonͳͲ : ྫ֎͕ൃੜ͢Δɻ Cݴޠ : ͨͱ͑͹fopenΛ࢖͏ͳΒ͹໭Γ஋͕NULLͱͳΓɺ errnoʹΤϥʔͷཧ༝͕ઃఆ͞ΕΔ(C++ͳΒྫ֎͕ൃੜ)ɻ

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ଟݴޠʹ͓͚ΔΤϥʔ 19 ର৅ Τϥʔ௨஌ Cݴޠ intͷฦΓ஋ͱͯ͠ΤϥʔΛฦ͢ fopen, java.util.Map.get() ͳͲ ฦΓ஋Λnullableͳܕʹͯ͠ɺΤϥʔ࣌ʹnullΛฦ͢ goݴޠͳͲ ฦΓ஋ΛΤϥʔͱͷλϓϧʹ͢Δ HaskellͷEitherܕͳͲ ฦΓ஋ΛΤϥʔͱͷ௚࿨ܕʹ͢Δ STLͷstreamͳͲ ΦϒδΣΫτΛΤϥʔঢ়ଶʹ͢Δ Java΍RubyɺPythonͳͲ ྫ֎Λ౤͛Δ

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ଟݴޠʹ͓͚ΔΤϥʔ 20 ֤ϓϩάϥϛϯάݴޠͷΤϥʔॲཧ͸ͦΕͧΕҟͳΔ͕ɺ ڞ௨తͳجຊతͳػೳ͕ଘࡏ͢Δɻ • Τϥʔॲཧ͸ϓϩάϥϜͷଓߦ·ͨ͸தஅΛ੍ޚͰ͖Δ • Τϥʔ͸ൃੜͨ͠ΤϥʔΛ֦ு͠৘ใΛิ଍͢Δ͜ͱ͕Ͱ͖Δ • ϢʔβʔఆٛͷΤϥʔΛ࣮૷Ͱ͖Δ

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GoͷΤϥʔϋϯυϦϯά 21

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࠷΋γϯϓϧͳΤϥʔϋϯυϦϯά 22

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Τϥʔܕ 23 Errorܕ͸Error()Λ࣋ͭΠϯλʔϑΣΠε

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Τϥʔܕ 24 Error()ͱ͍͏ৼΔ෣͍Λຬͨͤ͹ErrorܕͱͳΔ

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༨ஊ 25 Goͷඪ४ϥΠϒϥϦsyscallύοέʔδ͕ฦ͢errorܕ͸ɺ CݴޠͰΤϥʔΛѻ͏ͱ͖ʹొ৔͢Δerrnoͱಉ౳Ͱ͋ΓɺʢWindowsͷ৔߹͸GetLastError()ʣɺ ͦͷΤϥʔίʔυ͔ΒΤϥʔϝοηʔδΛಘΒΕΔErrorϝιουʢॲཧ͸strerrorɻWindowsͰ͸ FormatMessageʣΛ࣮૷ͨ͠Errnoܕͱ࣮ͯ͠૷͞Ε͍ͯΔɻ

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༨ஊ 26 Error͕ϑΟʔϧυͰ͸ͳ͘ϝιουͰ͋Δ͜ͱʹ͍ͭͯɺ Τϥʔϝοηʔδ͕ඞཁʹͳͬͨλΠϛϯά·Ͱ͜ͷจࣈྻԽʹ͔͔ΔίετΛ ௿ݮͤ͞ΒΕΔͱ͍͏఺ͰΑ͘ઃܭ͞Ε͍ͯΔɻ

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Τϥʔϥοϐϯά

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Τϥʔͷϥοϓ

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Τϥʔϥοϐϯάͱ͸ʁ 29 Τϥʔϥοϐϯά͸ΤϥʔΛϥοϓͯ͠ ݩͷΤϥʔ΋ར༻Ͱ͖ΔΑ͏ʹ͢Δ͜ͱ

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Τϥʔϥοϐϯάͱ͸ʁ 30 ಛఆͷϢʔβ͔Βσʔλϕʔεࢿݯ΁ͷΞΫηεཁٻΛड͚͕ͨɺΫΤϦத ʹʮύʔϛογϣϯ͕ڋ൱͞Ε·ͨ͠ʯͱ͍͏Τϥʔ͕ൃੜ͢Δͱ͖

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Τϥʔϥοϐϯάͱ͸ʁ 31 ͜͜Ͱจ຺৘ใΛ௥Ճ͢Δ୅ΘΓʹɺΤϥʔʹϚʔΫΛ͚͍ͭͨɻ ؔ਺Λݺͼग़ͨ͠ͱ͖ʹड͚ͱͬͨ͢΂ͯͷΤϥʔ͕ForbiddenܕՔಇԽΛݕࠪ͢ ΔHTTPϋϯυϥΛ࣮૷ͯ͠ɺ403Λฦ͢Α͏ʹ͢Δɻ

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Τϥʔϥοϐϯάͱ͸ʁ 32 ݺͼग़͠΋ͱ͸ɺΤϥʔΛΞϯϥοϓͯ͠ɺݩͷΤϥʔΛݕࠪ͢Δ͜ͱͰɺΤϥʔ Λॲཧ͢Δ͜ͱ͕Ͱ͖Δɻจ຺৘ใΛ௥Ճ্ͨ͠ͰɺϚʔΫ෇͚Λ͢Δͱ͍͏྆ํ ͷ৘ใΛሊԽ͍ͨ͠৔߹΋͋Δɻ

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ϥοϓ͠ͳ͍ 33

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ϥοϓ͠ͳ͍ 34

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ಠࣗͷΤϥʔܕ(Go1.13Ҏલ͸ओྲྀ) 35

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%w 36

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%v 37 %v͸%wͱҧͬͯϥοϓ͞Ε͓ͯΒͣɺม׵͞Ε͍ͯΔ͚ͩɻ →ݺͼग़͠ݩ͸͋ΜϥοϓͰ͖ͳ͍ɻݩͷΤϥʔ͸ར༻Ͱ͖ͳ͘ͳΔɻ

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%vΛ࢖ͬͯ͸͍͚ͳ͍ͷ͔ʁ 38 %wΑΓ੍ݶ͞Ε͍ͯΔ͕ɺඞͣ͠΋%wΛ࢖ͬͨ΄͏͕͍͍ͱ͸ݶΒͳ͍ɻ ΤϥʔΛϥοϓ͢Δͱɺݺͼग़͠ݩ͕ݩͷΤϥʔΛར༻Ͱ͖Δ͕ɺ ͦΕ͸ίʔυͷ݁߹ͱ͍͏જࡏతͳ໰୊Λಋೖͯ͠͠·͏ɻ ΤϥʔϥοϐϯάΛ࢖ͬͯݩͷΤϥʔ͕barΤϥʔ͔Ͳ͏͔ΛFooͷݺͼग़͠ݩ͕ݕࠪ͢Δ৔ ߹Λߟ͑Δɻͦͷ্Ͱ࣮૷Λมߋͯ͠ɺผͷؔ਺Λ࢖͍ɺผͷछྨͷΤϥʔΛฦ͢Α͏ʹ͢Δ ͱɺݺͼग़͠ݩ͕ߦͳͬͨΤϥʔͷݕ͕ࠪػೳ͠ͳ͘ͳΔɻ ΫϥΠΞϯτ͕࣮૷ͷৄࡉͱߟ͑ΒΕΔ΋ͷʹґଘ͠ͳ͍Α͏ʹ͢Δʹ͸ɺฦ͞ΕΔΤϥʔ͸ ϥοϓ͞ΕΔͷͰ͸ͳ͘ɺม׵͞ΕΔඞཁ͕͋Δɻ͜ͷΑ͏ͳ৔߹͸%wͰ͸ͳ͘ɺ%vΛ࢖༻ ͢Δͷ͕޷·͍͠ɻ

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pureͳ࣮૷ 39

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%w 40

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%v 41

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%v 42

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Τϥʔϥοϐϯά·ͱΊ 43 ํ๏ ௥Ճͷจ຺৘ใ ΤϥʔͷϚʔΫ෇͚ ݩͷΤϥʔ͕ར༻Մೳ ΤϥʔΛ௚઀ฦ͢ ❌ ❌ ⭕ ಠࣗͷΤϥʔܕ ⭕(Τϥʔܕ͕จࣈྻϑΟʔϧ υΛؚΜͰ͍ͨΒ) ⭕ ⭕(ݩͷΤϥʔ͕ެ։͞Ε͍ͯ ΔɺϝιουΛ௨ͯ͠ΞΫη εͰ͖ΔͳΒՄೳ) fmt.Errorfͱ%w ⭕ ❌ ⭕ fmt.Errorfͱ%v ⭕ ❌ ❌

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ΤϥʔͷΞϯϥοϓ

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Ξϯϥοϓ 45 Τϥʔܕ͕Unwrap()ͱ͍͏ৼΔ෣͍Λ͍࣋ͬͯΔͱ ݺͼग़͠ݩͰΞϯϥοϓ͢Δ͜ͱ͕Ͱ͖Δɻ Ξϯϥοϓ͢Δ͜ͱͰɺϥοϓ͞Εͨࡍͷ෇Ճ৘ใΛऔΓআ͖ɺ Τϥʔͷ৘ใΛऔಘͰ͖Δɻ

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Ξϯϥοϓ 46 ෇Ճ৘ใͷfoo failed:͕ग़ྗ͞Εͣ த਎͚ͩग़ྗ͞ΕΔɻ

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ݺͼग़͠ݩ 47 ݺͼग़͠ݩʹ͸err͕FooErrorܕͰ͋Δ͜ͱΛ ஌Βͳ͍ͷͰUnwrap()͕ଘࡏ͢Δ͜ͱ΋Θ͔Βͳ͍

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ܕΞαʔγϣϯ 48 iͷܕ͕TͰ͋Δ৔߹ɺ ok=true, tʹiͷ஋ΛΩϟετͯ͠୅ೖ i͕TͰͳ͍৔߹ɺok=false, tʹθϩ஋Λ୅ೖ(okΛলུ͢ΔͱɺpanicʹͳΔ)

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ܕΞαʔγϣϯ 49

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Ξϯϥοϓ 50

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Ξϯϥοϓ 51

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Τϥʔͷൺֱ

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errors.As()

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54 ϥοϓ͞ΕͨΤϥʔ͕ಛఆͷܕ͔൱͔ݕࠪ͢Δ errors.As

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errors.As 55 ΤϥʔΛ࠶ىతʹΞϯϥοϓ͠ɺ࿈࠯ͨ͠Τϥʔ͕ظ଴͢ΔܕʹҰக͢Δ৔߹ʹtrueΛฦ͢ɻ

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errors.As 56

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errors.Is()

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ηϯνωϧΤϥʔ 58 άϩʔόϧม਺ͱͯ͠ఆٛ͞ΕͨΤϥʔ

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ηϯνωϧΤϥʔ 59 ҰൠతʹɺErrXXXͱ໋໊͍ͬͨ͢Δɻ ηϯνωϧΤϥʔ͸༧ظ͞ΕΔΤϥʔΛ఻͑Δ΋ͷɻ

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error.Is() 60

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=Λ༻͍ͨ஋ͷൺֱ 61 fmt.Errorfͱ%wΛ࢖ͬͯsql.ErrNoRowsΛϥοϓ͢Δͱ err == sql.ErrNoRows ͸ৗʹfalseʹͳΔɻ

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=Λ༻͍ͨ஋ͷൺֱ 62

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ΤϥʔͷϥΠϒϥϦ

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ΤϥʔͷϥΠϒϥϦ 64 cockroach/errors : ਪ঑ɻෳ਺ΤϥʔରԠɻελοΫτϨʔε͋ΓɻݱࡏҰ൪ओྲྀͱͳͬͯΔ pkg/errors : archiveͳͷͰඇਪ঑ errors : ඪ४ϥΠϒϥϦɻϥοϐϯά͸ͳ͍ɻελοΫτϨʔεͳ͠ fmtͷErrof : ελοΫτϨʔεͳ͠ɻϰΝʔϒͰϥοϓ͢Δɻ%w, %v xerrors : ଟ͕͘Deprecatedʹͳ͍ͬͯΔͷͰඇਪ঑ hashicorp/go-multierror : ෳ਺ΤϥʔΛѻ͏ͨΊͷϥΠϒϥϦ͕ͩɺඪ४ϥΠϒϥϦͰରԠ͞Εͨ morikuni/failure : Τϥʔίʔυϕʔεͷྫ֎ϋϯυϦϯά go-errors/errors : ෳ਺Τϥʔʹ͸ରԠ͍ͯ͠Δ͕ɺػೳ΋ߋ৽ස౓΋ඍົͳͷͰඇਪ঑ goark/errs : ελοΫτϨʔε͋Γɻߋ৽ස౓͸ඍົ

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ͲͷϥΠϒϥϦ͕͍͍ͷ͔ 65 • ελοΫτϨʔε͕ඞཁͳ৔߹ : cockroach/errors • ελοΫτϨʔεΛ࢖Θͳ͍ͱ͖ : errors & fmt.Errof ͨͩ͠ɺελοΫτϨʔε͋Γͩͱ݁ߏύϑΥʔϚϯε͕མͪΔ

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cockroach/errors 66

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pkg/errors 67

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μϒϧϋϯυϦϯά

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69 Τϥʔϝοηʔδ͕ ϩάͷه࿥ͱฦ͞ΕΔΤϥʔͷ྆ํͰ܁Γฦ͞Ε͍ͯΔ ←Ң౓ͷ஋͕ແޮͷͱ͖

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70 Ͳͷݺͼग़͕ࣦ͠ഊͨ͠ͷ͔ͱ͍͏৘ใ͕ ࣦΘΕ͍ͯΔ

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71

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Τϥʔͷແࢹ

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Τϥʔͷແࢹ 73 ҙਤతʹΤϥʔϋϯυϦϯάΛল͍͍ͯΔ

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Τϥʔͷແࢹ 74 ແࢹ͢Δ৔߹͸্هͷํ๏Ұ୒ɻίϝϯτ౳͸৑௕

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͓·͚