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How to read code Shimpei Makimoto! 2014-09-24

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Shimpei Makimoto! Software Engineer photo by r7kamura @makimoto @makimoto

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Today's talk w )PXUPSFBEDPEF w &YBNQMFJNBHFQOHJOHPMBOHMJCT w 8IZHP  w TFMGDPOUBJOFE w TJNQMFMBOHVBHFTQFD w OFX w 8IZJNBHFQOH

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άϦονɾΞʔτΛ८ͬͯަΘ͞ΕΔٞ࿦ͷதʹ͸ɼάϦον͕ΘΕΘΕʹ༩͑Δ৺৅ͦ͜ຊ࣭ͩͱ͢Δཱ৔͕͋Γ·͢ɽͦͷཱ৔ ʹཱͭਓʑ͸ਅͷάϦον͸࠶ݱͰ͖ͳ͍ͱݴ͍ɼͦΕΒ͸ҰॠͰফ͑ڈΔͱݴ͍·͢ɽ࠶ݱͰ͖ͳ͍ͱओு͢ΔҎ্ɼ൴Β͸άϦο νɾΞʔτΛάϦονൈ͖Ͱߏ੒͠ͳͯ͘͸ͳΒͳ͍Ͱ͠ΐ͏ɽҰํͰɼϐΫηϧΛዞҙతʹฒͼସ͑ͨΓมܗͤͨ͞Γͨ͠ਤ૾Λ ΋ͬͯάϦονɾΞʔτͱ͢Δཱ৔͕͋Γ·͢ɽͦͷཱ৔͔ΒݟΔͱɼάϦονɾΞʔτͱ͸άϦονͷࢹ֮ޮՌΛϞνʔϑͱͨ͠ ਓ޻తͳΞʔτ࡞඼ͱ͍͏͜ͱʹͳΓ·͢ɽ ! ͜ͷɼ৺৅ͱͯ͠ͷάϦονͱϞνʔϑͱͯ͠ͷάϦον͸ɼάϦονͱ͍͏ݱ৅Λத৺ʹɼೋۃ΁ဃ཭͠ͳ͕ΒɼάϦονɾΞʔ τΛݻఆ͠͸͡Ί͍ͯ·͢ɽ͓ͦΒ͘কདྷతʹ͸ɼલऀͷओு͸άϦον࿦΍ඒֶͷจ຺΁ྲྀΕͯΏ͘Ͱ͠ΐ͏ɽޙऀ͸ΑΓҰൠత ͳҙຯͰάϦονɾΞʔτͷ໊Λ֫ಘͯ͠Ώ͘ʹҧ͍͋Γ·ͤΜɽάϦονɾϛϡʔδοΫͷઌྫʹؑΈͯ΋ɼͦΕ͸ࣗ͘͝વͳ੒ Γߦ͖ͩͱࢥΘΕ·͢ɽ VDOW   IUUQXXXOUUJDDPSKQ"SDIJWF0QFOTQBDF8PSLTUFYU@5BC@(MJUDI@KIUNM

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Step 0: Read the spec (roughly) w IUUQXXXXPSH531/( w 3FBEJUSPVHIMZ w *OPVSDBTF l$IVOL4QFDJpDBUJPOTzNBZ CFVTFGVM

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Step 1: Find files

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Step 2: Understand data structure (1) http://golang.org/src/pkg/image/png/reader.go

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Step 2: Understand data structure (2) http://golang.org/src/pkg/image/png/reader.go http://golang.org/pkg/image/

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Step 3: Specify important public methods http://golang.org/src/pkg/image/png/reader.go http://golang.org/pkg/image/png/

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Step 4: Reading w GVOD%FDPEF SJP3FBEFS  JNBHF*NBHF FSSPS  w GVOD E EFDPEFS DIFDL)FBEFS FSSPS w GVOD E EFDPEFS QBSTF$IVOL FSSPS w GVOD E EFDPEFS QBSTF*)%3 MFOHUIVJOU FSSPS w GVOD E EFDPEFS QBSTF1-5& MFOHUIVJOU FSSPS w GVOD E EFDPEFS QBSTFU3/4 MFOHUIVJOU FSSPS w GVOD E EFDPEFS QBSTF*%"5 MFOHUIVJOU  FSSFSSPS  w GVOD E EFDPEFS EFDPEF  JNBHF*NBHF FSSPS  w GVOD E EFDPEFS QBSTF*&/% MFOHUIVJOU FSSPS w GVOD E EFDPEFS WFSJGZ$IFDLTVN FSSPS

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func (d *decoder) decode() (image.Image, error) w TSDQLHJNBHFQOHHP w IUUQTHJTUHJUIVCDPNNBLJNPUP DGDGF

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wrap up w *OUSPEVDFEIPX*SFBEDPEF w 5PVOEFSTUBOEQPQVMBSBMHPSJUIN SFBEJOHMJCTJOHPMBOHJT WFSZIFMQGVM w *UPPLJNBHFQOHGPSBOFYBNQMF BOEUIFSF`SFNBOZ JNQMFNFOUTGPSQPQVMBSBMHPSJUINJOHPMBOH`TMJCT w *GZPVXBOUUPLOPX([JQDPNQSFTTJPO ZPVNBZSFBE DPNQSFTTH[JQ w *GZPVXBOUUPLOPX*1MPPLVQT ZPVNBZSFBEOFUMPPLVQ