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5෼ͰΘ͔Δ Kotlin Contracts 2019/10/01 potatotips #65 twitter.com/kumamo_tone

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• iOS/AndroidΤϯδχΞˏϠϑʔ • ษڧձӡӦ • Bonfire iOSɺWWDC Extended ͳͲ • ϠϑʔLODGEͰͷpotatotips͸4ճ໨ ۽ຊ ࿨ਖ਼ (@kumamo_tone)

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2019.08 Kotlin 1.3.50 2018.10 Kotlin 1.3 2019.? Kotlin 1.4 όʔδϣϯͷਪҠ

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2019.08 Kotlin 1.3.50 2018.10 Kotlin 1.3 2019.? Kotlin 1.4 όʔδϣϯͷਪҠ ৽ػೳ$POUSBDUT͕ొ৔

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2019.08 Kotlin 1.3.50 2018.10 Kotlin 1.3 2019.? Kotlin 1.4 όʔδϣϯͷਪҠ ·ͩ&YQFSJNFOUBM͕ͩɺ 4UEMJCͰ΋ͨ͘͞Μ࢖ΘΕ͍ͯΔ

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๩͍͠ਓͷͨΊͷ 5෼ͰΘ͔Δ Kotlin Contracts

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• ίϯύΠϥʹ໌ࣔతʹؔ਺ͷ;Δ·͍Λڭ͑Δ΋ͷ • ίϯύΠϥͷ੍໿Λ؇ΊΔ͜ͱ͕Ͱ͖Δ Contracts ͱ͸

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• ίϯύΠϥʹ໌ࣔతʹؔ਺ͷ;Δ·͍Λڭ͑Δ΋ͷ • ίϯύΠϥͷ੍໿Λ؇ΊΔ͜ͱ͕Ͱ͖Δ Contracts ͱ͸ ίϯύΠϥͷ੍໿ʁʁʁ

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εϚʔτΩϟετ fun getString(s: String?): String { return if (s == null || s.isEmpty()) { "ۭͩΑ" } else { s } }

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εϚʔτΩϟετ fun getString(s: String?): String { return if (s == null || s.isEmpty()) { "ۭͩΑ" } else { s } } s ͸ίϯύΠϥʹΑͬͯ String? ͔Β String ʹ Ωϟετ͞Ε͍ͯΔ

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εϚʔτΩϟετʹͳΒͳ͍ྫ fun String?.isNullOrEmpty(): Boolean { return this == null || this.isEmpty() } fun getString(s: String?): String { return if (s.isNullOrEmpty()) { "ۭͩΑ" } else { s } } ֦ுؔ਺ʹͯ͠Έͨ

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εϚʔτΩϟετʹͳΒͳ͍ྫ fun String?.isNullOrEmpty(): Boolean { return this == null || this.isEmpty() } fun getString(s: String?): String { return if (s.isNullOrEmpty()) { "ۭͩΑ" } else { s } } Type mismatch. Required: String Found: String? ίϯύΠϧΤϥʔ

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εϚʔτΩϟετʹͳΒͳ͍ྫ fun String?.isNullOrEmpty(): Boolean { return this == null || this.isEmpty() } fun getString(s: String?): String { return if (s.isNullOrEmpty()) { "ۭͩΑ" } else { s!! } }

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εϚʔτΩϟετʹͳΒͳ͍ྫ fun String?.isNullOrEmpty(): Boolean { return this == null || this.isEmpty() } fun getString(s: String?): String { return if (s.isNullOrEmpty()) { "ۭͩΑ" } else { s!! } }

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@kotlin.internal.InlineOnly public inline fun CharSequence?.isNullOrEmpty(): Boolean { contract { returns(false) implies (this@isNullOrEmpty != null) } return this == null || this.length == 0 }

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@kotlin.internal.InlineOnly public inline fun CharSequence?.isNullOrEmpty(): Boolean { contract { returns(false) implies (this@isNullOrEmpty != null) } return this == null || this.length == 0 } $POUSBDUʰʰܖ໿ʱʱ

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ʰ͜ͷؔ਺͕GBMTFΛฦ͢ͱ͖ɺ ͜ͷ$IBS4FRVFODF͸OVMMͰ͸ ͳ͍͜ͱΛอূ͢Δʂʱ @kotlin.internal.InlineOnly public inline fun CharSequence?.isNullOrEmpty(): Boolean { contract { returns(false) implies (this@isNullOrEmpty != null) } return this == null || this.length == 0 }

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@kotlin.internal.InlineOnly public inline fun CharSequence?.isNullOrEmpty(): Boolean { contract { returns(false) implies (this@isNullOrEmpty != null) } return this == null || this.length == 0 } ʰ͜ͷؔ਺͕GBMTFΛฦ͢ͱ͖ɺ ͜ͷ$IBS4FRVFODF͸OVMMͰ͸ ͳ͍͜ͱΛอূ͢Δʂʱ

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@kotlin.internal.InlineOnly public inline fun CharSequence?.isNullOrEmpty(): Boolean { contract { returns(false) implies (this@isNullOrEmpty != null) } return this == null || this.length == 0 } Θ͔ͬͨΑʙ ίϯύΠϥ

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fun getString(s: String?): String { return if (s.isNullOrEmpty()) { "ۭͩΑ" } else { s } } T͸OVMM͕อূ͞ΕͯΔͷͰ εϚʔτΩϟετ ͓͍ͯͨ͠Αʙ ίϯύΠϥ TPTNBSUʜʜ

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SVO XJUI BQQMZ BMTP είʔϓؔ਺ ࢛ఱԦ StdlibͰ͔ͭΘΕ͍ͯΔ΄͔ͷྫ

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val answer: Int run { answer = 42 } print(answer) run (Kotlin 1.2) ɺଖΕ͸ ੜ໋ɺӉ஦ɺͦͯ͠ສ෺ʹ͍ͭͯͷ ڀۃͷٙ໰ͷ౴͑ʜ ΫΫΫʜ

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run (Kotlin 1.2) ͳΜʜͩͱʜ ʢେৎ෉ͩͱࢥ͏Μ͚ͩͲͳʜʣ ෳ਺ճݺ͹ΕͨΒ ͋Ϳͳ͍Αʙ ίϯύΠϥ $PNQJMFSFSSPS $BQUVSFEWBMVFTJOJUJBMJ[BUJPO JTGPSCJEEFOEVFUPQPTTJCMFSFBTTJHONFOU val answer: Int run { answer = 42 } print(answer)

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@kotlin.internal.InlineOnly public inline fun T.run(block: T.() -> R) = block() @kotlin.internal.InlineOnly public inline fun T.run(block: T.() -> R): R { contract { callsInPlace(block, InvocationKind.EXACTLY_ONCE) } return block() } run (Kotlin 1.3)

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@kotlin.internal.InlineOnly public inline fun T.run(block: T.() -> R): R { contract { callsInPlace(block, InvocationKind.EXACTLY_ONCE) } return block() } $POUSBDUʰʰܖ໿ʱʱ

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@kotlin.internal.InlineOnly public inline fun T.run(block: T.() -> R): R { contract { callsInPlace(block, InvocationKind.EXACTLY_ONCE) } return block() } ʰ͜ͷϒϩοΫ͸ʜ ʰͨͬͨ౓ͷΈඞ࣮ͣߦ͞ΕΔʂʂʱʱ

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@kotlin.internal.InlineOnly public inline fun T.run(block: T.() -> R): R { contract { callsInPlace(block, InvocationKind.EXACTLY_ONCE) } return block() } Θ͔ͬͨΑʙ ίϯύΠϥ

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Ұ౓͔͠ݺ͹Εͳ͍ͳΒ ॳظԽͯ͠΋҆શ͔ͩΒɺ ڐՄ͓͍ͯͨ͠Αʙ ίϯύΠϥ TPTNBSUʜʜ val answer: Int run { answer = 42 } print(answer)

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ݴ༿ʹ͠ͳ͍ͱɺ఻ΘΒͳ͍͜ͱ΋͋Δʢʁʁʁʣ http://gahag.net/001427-businessman-handshake/

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• Contractsͱ͸ • Kotlin 1.3 Ͱ௥Ճ͞ΕͨػೳʢExperimentalʣ • isNullOrEmpty/run/with/apply/alsoͳͲStdlibͰଟ਺࢖ΘΕ͍ͯΔ • ίϯύΠϥʹ໌ࣔతʹؔ਺ͷ;Δ·͍Λڭ͑Δ͜ͱͰɺ
 ίϯύΠϥͷ੍໿Λ؇ΊΔ͜ͱ͕Ͱ͖Δ ·ͱΊ

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• What’s New in Kotlin 1.3 • https://kotlinlang.org/docs/reference/whatsnew13.html • What's new in Kotlin? • https://speakerdeck.com/svtk/whats-new-in-kotlin • վΊֶͯͿContracts • https://speakerdeck.com/tommykw/gai-metexue-hucontracts References