5分でわかる Kotlin Contracts

potatotips #65 での発表資料です。
https://potatotips.connpass.com/event/145538/

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

改めて学ぶContracts
https://speakerdeck.com/tommykw/gai-metexue-hucontracts

Transcript

1. 5෼ͰΘ͔Δ Kotlin Contracts 2019/10/01 potatotips #65 twitter.com/kumamo_tone
2. • iOS/AndroidΤϯδχΞˏϠϑʔ • ษڧձӡӦ • Bonfire iOSɺWWDC Extended ͳͲ • ϠϑʔLODGEͰͷpotatotips͸4ճ໨ ۽ຊ ࿨ਖ਼ (@kumamo_tone)
3. 2019.08 Kotlin 1.3.50 2018.10 Kotlin 1.3 2019.? Kotlin 1.4 όʔδϣϯͷਪҠ
4. 2019.08 Kotlin 1.3.50 2018.10 Kotlin 1.3 2019.? Kotlin 1.4 όʔδϣϯͷਪҠ ৽ػೳ
   $POUSBDUT
   ͕ొ৔
5. 2019.08 Kotlin 1.3.50 2018.10 Kotlin 1.3 2019.? Kotlin 1.4 όʔδϣϯͷਪҠ ·ͩ&YQFSJNFOUBM͕ͩɺ
   4UEMJCͰ΋ͨ͘͞Μ࢖ΘΕ͍ͯΔ
6. ๩͍͠ਓͷͨΊͷ 5෼ͰΘ͔Δ Kotlin Contracts
7. • ίϯύΠϥʹ໌ࣔతʹؔ਺ͷ;Δ·͍Λڭ͑Δ΋ͷ • ίϯύΠϥͷ੍໿Λ؇ΊΔ͜ͱ͕Ͱ͖Δ Contracts ͱ͸
8. • ίϯύΠϥʹ໌ࣔతʹؔ਺ͷ;Δ·͍Λڭ͑Δ΋ͷ • ίϯύΠϥͷ੍໿Λ؇ΊΔ͜ͱ͕Ͱ͖Δ Contracts ͱ͸ ίϯύΠϥͷ੍໿ʁʁʁ
9. εϚʔτΩϟετ fun getString(s: String?): String { return if (s == null || s.isEmpty()) { "ۭͩΑ" } else { s } }
10. εϚʔτΩϟετ fun getString(s: String?): String { return if (s == null || s.isEmpty()) { "ۭͩΑ" } else { s } } s ͸ίϯύΠϥʹΑͬͯ String? ͔Β String ʹ Ωϟετ͞Ε͍ͯΔ
11. εϚʔτΩϟετʹͳΒͳ͍ྫ fun String?.isNullOrEmpty(): Boolean { return this == null || this.isEmpty() } fun getString(s: String?): String { return if (s.isNullOrEmpty()) { "ۭͩΑ" } else { s } } ֦ுؔ਺ʹͯ͠Έͨ
12. 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
13. εϚʔτΩϟετʹͳΒͳ͍ྫ fun String?.isNullOrEmpty(): Boolean { return this == null || this.isEmpty() } fun getString(s: String?): String { return if (s.isNullOrEmpty()) { "ۭͩΑ" } else { s!! } }
14. εϚʔτΩϟετʹͳΒͳ͍ྫ fun String?.isNullOrEmpty(): Boolean { return this == null || this.isEmpty() } fun getString(s: String?): String { return if (s.isNullOrEmpty()) { "ۭͩΑ" } else { s!! } }
15. @kotlin.internal.InlineOnly public inline fun CharSequence?.isNullOrEmpty(): Boolean { contract { returns(false) implies (this@isNullOrEmpty != null) } return this == null || this.length == 0 }
16. @kotlin.internal.InlineOnly public inline fun CharSequence?.isNullOrEmpty(): Boolean { contract { returns(false) implies (this@isNullOrEmpty != null) } return this == null || this.length == 0 } $POUSBDU
    ʰʰܖ໿ʱʱ
17. ʰ͜ͷؔ਺͕GBMTFΛฦ͢ͱ͖ɺ
    ͜ͷ$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 }
18. @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
19. @kotlin.internal.InlineOnly public inline fun CharSequence?.isNullOrEmpty(): Boolean { contract { returns(false) implies (this@isNullOrEmpty != null) } return this == null || this.length == 0 } Θ͔ͬͨΑʙ ίϯύΠϥ
20. fun getString(s: String?): String { return if (s.isNullOrEmpty()) { "ۭͩΑ" } else { s } } T͸OVMM͕อূ͞ΕͯΔͷͰ
    εϚʔτΩϟετ
    ͓͍ͯͨ͠Αʙ ίϯύΠϥ TP
    TNBSU
    ʜʜ
21. SVO XJUI BQQMZ BMTP είʔϓؔ਺
    ࢛ఱԦ StdlibͰ͔ͭΘΕ͍ͯΔ΄͔ͷྫ
22. val answer: Int run { answer = 42 } print(answer) run (Kotlin 1.2) ɺଖΕ͸
    ੜ໋ɺӉ஦ɺͦͯ͠ສ෺ʹ͍ͭͯͷ
    ڀۃͷٙ໰ͷ౴͑ʜ
    ΫΫΫʜ
23. run (Kotlin 1.2) ͳΜʜͩͱʜ
    ʢେৎ෉ͩͱࢥ͏Μ͚ͩͲͳʜʣ ෳ਺ճݺ͹ΕͨΒ
    ͋Ϳͳ͍Αʙ ίϯύΠϥ $PNQJMFS
    FSSPS
    $BQUVSFE
    WBMVFT
    JOJUJBMJ[BUJPO
    JT
    GPSCJEEFO
    EVF
    UP
    QPTTJCMF
    SFBTTJHONFOU val answer: Int run { answer = 42 } print(answer)
24. @kotlin.internal.InlineOnly public inline fun <T, R> T.run(block: T.() -> R) = block() @kotlin.internal.InlineOnly public inline fun <T, R> T.run(block: T.() -> R): R { contract { callsInPlace(block, InvocationKind.EXACTLY_ONCE) } return block() } run (Kotlin 1.3)
25. @kotlin.internal.InlineOnly public inline fun <T, R> T.run(block: T.() -> R): R { contract { callsInPlace(block, InvocationKind.EXACTLY_ONCE) } return block() } $POUSBDU
    ʰʰܖ໿ʱʱ
26. @kotlin.internal.InlineOnly public inline fun <T, R> T.run(block: T.() -> R): R { contract { callsInPlace(block, InvocationKind.EXACTLY_ONCE) } return block() } ʰ͜ͷϒϩοΫ͸ʜ
    ʰͨͬͨ౓ͷΈඞ࣮ͣߦ͞ΕΔʂʂʱʱ
27. @kotlin.internal.InlineOnly public inline fun <T, R> T.run(block: T.() -> R): R { contract { callsInPlace(block, InvocationKind.EXACTLY_ONCE) } return block() } Θ͔ͬͨΑʙ ίϯύΠϥ
28. Ұ౓͔͠ݺ͹Εͳ͍ͳΒ
    ॳظԽͯ͠΋҆શ͔ͩΒɺ
    ڐՄ͓͍ͯͨ͠Αʙ ίϯύΠϥ TP
    TNBSU
    ʜʜ val answer: Int run { answer = 42 } print(answer)
29. ݴ༿ʹ͠ͳ͍ͱɺ఻ΘΒͳ͍͜ͱ΋͋Δʢʁʁʁʣ http://gahag.net/001427-businessman-handshake/
30. • Contractsͱ͸ • Kotlin 1.3 Ͱ௥Ճ͞ΕͨػೳʢExperimentalʣ • isNullOrEmpty/run/with/apply/alsoͳͲStdlibͰଟ਺࢖ΘΕ͍ͯΔ • ίϯύΠϥʹ໌ࣔతʹؔ਺ͷ;Δ·͍Λڭ͑Δ͜ͱͰɺ
 ίϯύΠϥͷ੍໿Λ؇ΊΔ͜ͱ͕Ͱ͖Δ ·ͱΊ
31. • 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