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
   

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

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3. 2019.08
   Kotlin 1.3.50
   2018.10
   Kotlin 1.3
   2019.?
   Kotlin 1.4
   όʔδϣϯͷਪҠ
   

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4. 2019.08
   Kotlin 1.3.50
   2018.10
   Kotlin 1.3
   2019.?
   Kotlin 1.4
   όʔδϣϯͷਪҠ
   ৽ػೳ$POUSBDUT͕ొ৔
   

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5. 2019.08
   Kotlin 1.3.50
   2018.10
   Kotlin 1.3
   2019.?
   Kotlin 1.4
   όʔδϣϯͷਪҠ
   ·ͩ&YQFSJNFOUBM͕ͩɺ
   4UEMJCͰ΋ͨ͘͞Μ࢖ΘΕ͍ͯΔ
   

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6. ๩͍͠ਓͷͨΊͷ
   5෼ͰΘ͔Δ Kotlin Contracts
   

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

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

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

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10. 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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11. 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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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
    

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13. 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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14. 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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15. @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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16. @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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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
    }
    

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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
    

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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
    

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

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21. SVO XJUI
    BQQMZ
    BMTP
    είʔϓؔ਺
    ࢛ఱԦ
    StdlibͰ͔ͭΘΕ͍ͯΔ΄͔ͷྫ
    

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

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23. 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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24. @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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25. @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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26. @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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27. @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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28. Ұ౓͔͠ݺ͹Εͳ͍ͳΒ
    ॳظԽͯ͠΋҆શ͔ͩΒɺ
    ڐՄ͓͍ͯͨ͠Αʙ
    ίϯύΠϥ
    TPTNBSUʜʜ
    val answer: Int
    run {
    answer = 42
    }
    print(answer)
    

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

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30. • Contractsͱ͸
    • Kotlin 1.3 Ͱ௥Ճ͞ΕͨػೳʢExperimentalʣ
    • isNullOrEmpty/run/with/apply/alsoͳͲStdlibͰଟ਺࢖ΘΕ͍ͯΔ
    • ίϯύΠϥʹ໌ࣔతʹؔ਺ͷ;Δ·͍Λڭ͑Δ͜ͱͰɺ

    ίϯύΠϥͷ੍໿Λ؇ΊΔ͜ͱ͕Ͱ͖Δ
    ·ͱΊ
    

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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
    

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