Carefully use and Enjoy Static Extension Methods

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4UBUJD&YUFOTJPO.FUIPET  ࢖͏લʹ஌͓͖͍ͬͯͨ஫ҙॻ͖ 2019.11.7. Flutter Meetup Tokyo #12 @makicamel

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ࣗݾ঺հ •@makicamel / ઒ݪສق •Flutterྺ൒೥͘Β͍ •Ruby ͱϏʔϧɹɹͱ͓ञ͕޷͖

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ࣗݾ঺հ

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•ڥք஋ͱͯ͠ࠓ೔ਂ໷0࣌ͷDateTimeΠϯελϯε͕΄͍͠ DateCalc.now().beginningOfDay(); •aͱb͕ಉ͡೔͔Ͳ͏͔൑ఆ͍ͨ͠ a.isSameDay(b); •c͕Կϲ݄લͳͷ͔Λऔಘ͍ͨ͠ c.differenceValue(type: DateType.month); •1೥ޙͷࠓ೔ͷ೔෇Λग़͍ͨ͠ DateCalc.now().addYear(1); DateCalc

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Dart 2.6 is available IUUQTEBSUEFW

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IUUQTUXJUUFSDPNEBSU@MBOHTUBUVT

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Static Extension Methods %BSU4UBUJD&YUFOTJPO.FUIPET%FTJHOEBSUMBOHMBOHVBHFc(JU)VC  IUUQTHJUIVCDPNEBSUMBOHMBOHVBHFCMPCFEDDCEBD⒎DD BDDFQUFEGVUVSFSFMFBTFTTUBUJDFYUFOTJPONFUIPETGFBUVSFTQFDJpDBUJPONE

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Static Extension Methods ? •طଘͷClassΛมߋɾ֦ு(Extend)͢Δߏจ ɹɹɹ֦ுؔ਺ ɹɹɹΤΫεςϯγϣϯ/Extension ɹɹɹΦʔϓϯΫϥε

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DateFormat('yyyy/MM/dd'). format(DateTime.now().add(Duration(days: 1))); ͜Ε·Ͱ •௕͍ •ͱ͘ʹ3͕ಡΈͮΒ͍ ᶃ ᶄ ᶅ ɹ໌೔ͷ೔෇ͷจࣈྻΛऔಘ͍ͨ͠

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doMyOtherStuff(doMyStuff(obj.doStuff()).doOtherStuff()); ᶃ ͜Ε·Ͱ ᶄ ᶅ ᶆ ᶅ

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(DateTime.now() + 1.days).toString('yyyy/MM/dd'); ͜Ε͔Β •γϯϓϧ DateTime.tomorrow().toString('yyyy/MM/dd'); ɹ໌೔ͷ೔෇ͷจࣈྻΛऔಘ͍ͨ͠

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obj.doStuff().doMyStuff().doOtherStuff().doMyOtherStuff(); ͜Ε͔Β

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4UBUJD&YUFOTJPO5ZQFTEBSUMBOHMBOHVBHFc(JU)VC  IUUQTHJUIVCDPNEBSUMBOHMBOHVBHFJTTVFT Static Extension Methods •Readability  (Մಡੑ) •Discoverability(IDE Support)  (ൃݟ༰қੑ(IDEͷαδΣετΛड͚΍͍͢)) • Static Extension Types • Pipeline-operator ɹ΋ݕ౼த 1JQFMJOFPQFSBUPSGPSJOMJOFJOWPDBUJPOPGTUBUJDGVODUJPOTEBSUMBOHMBOHVBHFc(JU)VC  IUUQTHJUIVCDPNEBSUMBOHMBOHVBHFJTTVFT

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How to try it IUUQTUXJUUFSDPN@NPOPTUBUVT stableҎ֎Ͱ2.6.0Ҏ্ͷਖ਼ࣜ൛͕ೖΓ·ͨ͠

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1. flutter channel ɹࣗ෼ͷνϟϯωϧΛ֬ೝ   3 steps to try it ❯ flutter channel Flutter channels: beta dev master * stable ͠͹Β͘upgrade͍ͯ͠ͳ͍ਓ͸ ﬂutter upgrade ΋ ﬂutter upgrade

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2. flutter channel master ɹνϟϯωϧ͕stableͳΒ੾Γସ͑   3 steps to try it ❯ flutter channel master Switching to flutter channel 'master'... git: From https://github.com/flutter/flutter git: 55df81e8e..28b5cc382 git: master -> origin/master git: Switched to branch 'master'

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3. flutter --version ɹμ΢ϯϩʔυͱϏϧυΛ૸ΒͤΔ   3 steps to try it ❯ flutter --version Flutter 1.10.15-pre.419 • channel master • https://github.com/flutter/flutter.git Framework • revision 02aac5072c (11 hours ago) • 2019-11-05 14:38:09 -0800 Engine • revision 0928c1af2f Tools • Dart 2.7.0 ४උ׬ྃ

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Static Extension Methodsͷߏจ extension ExtensionSupporterNum on Num { Duration get days => milliseconds * Duration.millisecondsPerDay; } Ϋϥε໊ ֦ுΫϥε໊͸࣮ࡍ࢖Θͳ͍ͷͰ িಥ͠ʹ໊͍͘લʹ͢Δ

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extension ExtensionSupporterNum on Num { Duration get days => milliseconds * Duration.millisecondsPerDay; } 1.days

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1.days 1.days // => 24:00:00.000000

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ϋϚΓͲ͜Ζ •Πϯελϯεม਺͸௥ՃͰ͖ͳ͍ •NNBD(Non-Null by Default; null҆શ)  Ͱͳ͍ม਺ͷnull͸֦ுͰ͖ͳ͍ •ϝιου໊ͷিಥʹ஫ҙ

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ϋϚΓͲ͜Ζ •Πϯελϯεม਺͸௥ՃͰ͖ͳ͍ •NNBD(Non-Null by Default; null҆શ)  Ͱͳ͍ม਺ͷnull͸֦ுͰ͖ͳ͍ •ϝιου໊ͷিಥʹ஫ҙ

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DateTime() + 1.month •`+` ͷҾ਺ʹΑͬͯݺͿॲཧΛม͍͑ͨ •1.daysͷͱ͖ɿDateTime().addΛݺͼ͍ͨ •1.monthsͷͱ͖ɿDateTime().addMonthΛݺͼ͍ͨ •Duration͸microsecondsͷ֓೦ɺ୯Ґ͸͍࣋ͬͯͳ͍ •ੜ੒࣌ʹdaysͱmonthsͷͲͪΒ͕౉͞Ε͔ͨΘ͔Βͳ͍

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•DuraionʹtypeΛ࣋ͨͤΕ͹͍͍ͷͰ͸ extension ExtensionSupporterDuration on Duration { DurationType type; } •Πϯελϯεม਺͸௥ՃͰ͖ͳ͍ •(Ϋϥεม਺͸௥ՃͰ͖Δ) DateTime() + 1.month

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•ͳͷͰ͜͏ͨ͠ class DurationMonth extends Duration { int months; DurationMonth({this.months = 0}) : super(); } extension ExtensionSupporterNum on num { DurationMonth get months => DurationMonth(months: toInt()); } DateTime() + 1.month

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•ͳͷͰ͜͏ͨ͠ extension ExtensionSupporterDateTime on DateTime { DateTime operator +(DurationMonth duration) { if (duration.runtimeType == DurationMonth) { return addMonth(duration.months); } return add(duration); } } IUUQTHJUIVCDPNNBLJDBNFMFYUFOTJPO@TVQQPSUFS ͥͻΞυόΠε͍ͩ͘͞ DateTime() + 1.month

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ϋϚΓͲ͜Ζ •Πϯελϯεม਺͸௥ՃͰ͖ͳ͍ •NNBD(Non-Null by Default; null҆શ)  Ͱͳ͍ม਺ͷnull͸֦ுͰ͖ͳ͍ •ϝιου໊ͷিಥʹ஫ҙ

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NNBD •௕͍ •ಉ͜͡ͱԿճ΋ॻ͖ͨ͘ͳ͍ if (user.containsKey('someList') && user['someList'].isNotEmpty()) { ... }

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NNBD extension MyNull on Null { bool get isEmpty => true; } null.isEmpty; // => true final user = {'name': 'makicamel'}; user['someList'].isEmpty; // Unhandled exception: // NoSuchMethodError: // The getter 'isEmpty' was called on null.

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NNBD where a legacy unsafely nullable type may   contain null ,  it is a run-time error if a migrated extension with a   non-nullable on type is called on null %BSU4UBUJD&YUFOTJPO.FUIPET%FTJHOEBSUMBOHMBOHVBHFc(JU)VC  IUUQTHJUIVCDPNEBSUMBOHMBOHVBHFCMPCFEDDCEBD⒎DD BDDFQUFEGVUVSFSFMFBTFTTUBUJDFYUFOTJPONFUIPETGFBUVSFTQFDJpDBUJPONE ैདྷͷnullableͳܕʹnullؚ͕·ΕΔ৔߹ɺ  nullෆՄͷܕͷExtension͕nullͰݺ͹ΕΔͱ  ࣮ߦ࣌ΤϥʔʹͳΓ·͢ &YUFOEͰ͖ͳ͍

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ϋϚΓͲ͜Ζ •Πϯελϯεม਺͸௥ՃͰ͖ͳ͍ •NNBD(Non-Null by Default; null҆શ)  Ͱͳ͍ม਺ͷnull͸֦ுͰ͖ͳ͍ •ϝιου໊ͷিಥʹ஫ҙ

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ϝιου໊ͷিಥ extension ListT on List { void best() => print('bestT'); } extension ListInt on List { void best() => print('bestInt'); } ίϯύΠϧΤϥʔʹͳΒͳ͍  ʢͪͳΈʹ'bestT'͕ฦͬͯ͘Δ)

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ϝιου໊ͷিಥ extension ListT on List { void best() => print('bestT'); } extension ListNum on List { void best() => print('bestNum'); } // => Error: The method 'best' isn't defined // for the class 'List'. ৄࡉ౓͕ಉ͡Extension͕ఆٛ͞Ε͍ͯΔͱ  ίϯύΠϧΤϥʔʹͳΔ

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ϝιου໊ͷিಥ [1].best(); extension ListInt on List { void best() => print('bestInt'); } extension ListT on List { void best() => print('bestT'); } extension ListNum on List { void best() => print('bestNum'); } extension ListNone on List { void best() => print('bestNone'); } ͨ͠৔߹ɺ্͕ڧ͍ˡˠԼ͕ऑ͍

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•ৄࡉ౓Λߟ͑࢝ΊΔઃܭ͸Կ͔͕ؒҧ͍ͬͯΔ ϝιου໊ͷিಥ

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ͭ·Γ

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•૝ఆͨ͠ڍಈͱҧ͏ڍಈΛ͢ΔՄೳੑ͕͋Δ •ؒ઀తʹ֦ு͞Ε͍ͯΔͱมߋʹؾ͖ͮʹ͍͘ •໊લ͕িಥͨ࣌͠ʹยํ͕༏ઌ౓ͷ໰୊Ͱෛ͚Δ •໊લ͕িಥͨ࣌͠ʹ༏ઌ౓͕ಉ͡ͰΤϥʔʹͳΔ •ؒ઀తʹ֦ு͞Ε͍ͯΔͱিಥʹؾ͖ͮʹ͍͘ •ϥΠϒϥϦಉ࢜Ͱ֦ு͕িಥ͢Δͱղܾ͕ࠔ೉ •☝Λௐ੔͠Α͏ͱͯ͠ͳίʔυ͕ੜ·Ε΍͍͢ Ϋϥεͷڍಈͷมߋ͸ةݥ

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•ΞϓϦέʔγϣϯίʔυͰͷར༻͸ϧʔϧܾΊ͕େࣄ •extensionsσΟϨΫτϦΛ੾ִͬͯ཭ •ϑΝΠϧΛࡉ͔͘෼͚ͯখ͘͞importͰ͖ΔΑ͏ʹ͢Δ •APIΛ૿΍͢৔߹͸νʔϜ಺Ͱ໋໊نଇΛઃఆ •( ͔ͿΓͦ͏ͳ໊લ͸࣌ݶര஄ ) •ϥΠϒϥϦͷόάͳͲҰ࣌తͳύονͷ৔߹͸APIΛมߋ ͠ͳ͍ •ͦ΋ͦ΋ແҋʹߦ͏΋ͷͰ͸ͳ͍ Ϋϥ εͷڍಈͷมߋ͸ةݥʁ

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ϥΠϒϥϦ࡞੒࣌ͷํ਑ •֦ுͨ͠ϝιουΛAPIͱͯ͠ఏڙ͠ͳ͍৔߹ •ϝιου໊ͷϓϨϑΟοΫεΛύοέʔδ໊ʹ͢ΔͳͲ ͷϧʔϧ͕͋Δͱ҆৺ͦ͏ •֦ுͨ͠APIΛఏڙ͢Δ৔߹ DateTime.now() + 1.months; •ϝιου໊ࣗମʹҙຯ͕͋Δ •ϑΝΠϧΛࡉ͔͘෼Θ͚Δ͘Β͍ͷରࡦ͔ͱ…

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•஫ҙ఺ •Πϯελϯεม਺͸௥ՃͰ͖ͳ͍ •null҆શͰͳ͍ม਺ͷnull͸֦ுͰ͖ͳ͍ •ϝιου໊ͷিಥʹ஫ҙ •Static Extension Methods͸͍͍ͧ •௒؆୯ʹ࢝ΊΒΕΔ •ඪ४Ϋϥεʹϝιου௥ՃͰ͖Δͷָ͍͠ʂ ·ͱΊ