こんなに違う！ScalaとKotlin

Arrow
https://github.com/arrow-kt/arrow

Kotlin Puzzler
https://github.com/angryziber/kotlin-puzzlers

Transcript

1. What a difference!
   
   @kaelaela
   

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2. kaelaela(まえかわ ゆういち)
   Backend engineer at アルプ株式会社/Alp, Inc
   Work: Scala with DDD with Eff
   Twitter: _kaelaela
   GitHub: kaelaela
   Scala: helf a year
   Kotlin: 2.5 years
   

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3. Scala == Kotlin
   ???
   ScalaとKotlinは同じ？
   

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4. Kotlin extends Scala
   ???
   KotlinはScalaを真似して作られた？
   

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5. Scala philosophy / Scalaの哲学
   Scalable language
   スケーラブルな言語
   Unifies object-oriented and functional programming
   オブジェクト指向と関数型の統合
   Interoperates seamlessly with Java
   Javaとのシームレスな相互運用
   

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6. Kotlin philosophy / Kotlinの哲学
   健全性よりも
   

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7. Scala != Kotlin
   ???
   ScalaとKotlinは全然違う？
   

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8. Scala and Kotlin are similar
   data class User(
   var name: String = "anonymous"
   )
   似てる！
   case class User(
   name: String = "anonymous"
   )
   

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9. Scala and Kotlin are VERY similar
   data class User...
   val user = User().apply {
   name = "yuichi"
   }
   println(user.name)
   // yuichi
   case class User...
   val user = User.apply(
   name = "yuichi"
   )
   println(user.name)
   // yuichi
   めっちゃ似てる！
   

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10. Scala
    case class User...
    val user = User.apply(
    name = "yuichi"
    )
    println(user.name)
    // yuichi
    Tiny diff…?
    Kotlin
    data class User...
    val user = User().apply {
    name = "yuichi"
    }
    println(user.name)
    // yuichi
    ﾁｮｯﾄ違う…？
    

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11. case class User…
    object User {
    def apply(name: String): User = new User(name)
    def main(args: Array[String]) = {
    val user = User.apply(name = "yuichi")
    println(user.name)
    }
    }
    How is the class defined?
    data class User…
    fun main() {
    val user = User().apply {name = "yuichi"}
    println(user.name)
    } クラスはどう？
    

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12. case class User…
    object User {
    def apply(name: String): User = new User(name)
    def main(args: Array[String]) = {
    val user = User.apply(name = "yuichi")
    println(user.name)
    }
    }
    data class User…
    fun main() {
    val user = User().apply {name = "yuichi"}
    println(user.name)
    }
    Very different...
    全然違う…
    

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13. case class User…
    object User {
    def apply(name: String): User = new User(name)
    def main(args: Array[String]) = {
    val user = User.apply(name = "yuichi")
    println(user.name)
    }
    }
    data class User…
    fun main() {
    val user = User().apply {name = "yuichi"}
    println(user.name)
    } KotlinはObjectがなくていい
    Top level function(Kotlin)
    

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14. case class User…
    object User {
    def apply(name: String): User = new User(name)
    def main(args: Array[String]) = {
    val user = User.apply(name = "yuichi")
    println(user.name)
    }
    }
    data class User…
    fun main() {
    val user = User().apply {name = "yuichi"}
    println(user.name)
    }
    Apply function
    Scope function
    Kotlinのapplyはスコープ関数
    Different function
    

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15. How is Scala code decompiled?
    public void main(final String[] args) {
    User user = User$.MODULE$.apply("yuichi");
    .MODULE$.println(user.name());
    }
    Scalaをデコンパイルするとシンプル
    

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16. How is Kotlin code decompiled?
    public final class UserKt {
    public static final void main() {
    User var1 = new User((String)null, 1, (DefaultConstructorMarker)null);
    ~~~ // some variables by scope function
    var1.setName("yuichi");
    String var6 = var1.getName();
    ~~~
    System.out.println(var6);
    }
    public static void main(String[] var0) { main(); }
    }
    Kotlinをデコンパイルすると？
    

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17. Top level function == ~~Kt class
    public final class UserKt {
    public static final void main() {
    User var1 = new User((String)null, 1, (DefaultConstructorMarker)null);
    ~~~
    var1.setName("yuichi");
    String var6 = var1.getName();
    ~~~
    System.out.println(var6);
    }
    public static void main(String[] var0) { main(); }
    }
    関数をトップにするとXXXKtクラスが自動生成
    

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18. How to show decompile code?(IntelliJ IDEA)
    IDEAでデコンパイル
    

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19. How to show decompile code?(AS)
    ASでデコンパイル
    

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20. Kotlin
    fun main() {
    val list = listOf(1)
    when (list) {
    is MutableList -> {
    val add = list += 2
    println("$add")
    }
    }
    }
    // ???
    Scala
    def main(args: ...): Unit = {
    val list = MutableList(1)
    list match {
    case MutableList(_) => {
    val add = list += 2
    println(s"$add")
    }
    }
    }
    // ???
    List
    Kotlin puzzlers
    https://github.com/angryziber/kotlin-puzzlers
    

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21. Kotlin
    fun main() {
    val list = listOf(1)
    when (list) {
    is MutableList -> {
    val add = list += 2
    println("$add")
    }
    }
    }
    // UnsupportedOperationException
    Scala
    def main(args: ...): Unit = {
    val list = MutableList(1)
    list match {
    case MutableList(_) => {
    val add = list += 2
    println(s"$add")
    }
    }
    }
    // MutableList(1, 2)
    List
    

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22. Kotlin
    fun main() {
    val list = listOf(1) // ArrayList!!!
    when (list) {
    is MutableList -> {
    val add = list += 2
    println("$add")
    }
    }
    }
    // UnsupportedOperationException
    Scala
    def main(args: ...): Unit = {
    val list = MutableList(1)
    list match {
    case MutableList(_) => {
    val add = list += 2
    println(s"$add")
    }
    }
    }
    // MutableList(1, 2)
    List
    KotlinのlistOfはArrayList
    

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23. Kotlin cannot FP
    ???
    Kotlinでは関数型ができないでしょうか
    

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24. Arrow
    > Functional companion to Kotlin's Standard Library
    Option
    Either
    Try
    NonEmptyList
    Validated
    ...
    ArrowはKotlinの関数型実装をもつライブラリです
    

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25. Arrow
    > Functional companion to Kotlin's Standard Library
    Option
    Either
    Try
    NonEmptyList
    Validated
    ...
    Default in Scala
    

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26. Arrow
    > Functional companion to Kotlin's Standard Library
    Option
    Either
    Try
    NonEmptyList
    Validated
    ...
    Cats/Scalaz
    

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27. Arrow
    > Functional companion to Kotlin's Standard Library
    Option
    Either
    Try
    NonEmptyList
    Validated
    ...
    Cats/Scalaz
    

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28. Scala/Cats
    val list = NonEmptyList.of(1, 2, 3)
    val tail = list ++ List(100)
    println(s"${tail.exists(_ == 1)}")
    // ???
    println(s"${tail.exists(_ == 100)}")
    // ???
    Check element of NonEmptyList
    Kotlin/Arrow
    val list = NonEmptyList.of(1, 2, 3)
    val tail = list + listOf(100)
    println("${tail.contains(1)}")
    // ???
    println("${tail.contains(100)}")
    // ???
    CatsとArrowの要素チェック
    

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29. The same results
    Kotlin/Arrow
    val list = NonEmptyList.of(1, 2, 3)
    val tail = list + listOf(100)
    println("${tail.contains(1)}")
    // true
    println("${tail.contains(100)}")
    // true
    Scala/Cats
    val list = NonEmptyList.of(1, 2, 3)
    val tail = list ++ List(100)
    println(s"${tail.exists(_ == 1)}")
    // true
    println(s"${tail.exists(_ == 100)}")
    // true
    結果は同じ
    

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30. Cats => Scalaz
    Kotlin/Arrow
    val list = NonEmptyList.of(1, 2, 3)
    val tail = list + listOf(100)
    println("${tail.contains(1)}")
    // true
    println("${tail.contains(100)}")
    // true
    Scala/Scalaz
    val list = NonEmptyList(1, 2, 3)
    val tail = list +: List(100)
    println(s"${tail.contains(1)}")
    // ???
    println(s"${tail.contains(100)}")
    // ???
    ScalazとArrow
    

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31. NOT the same results :-o
    Kotlin/Arrow
    val list = NonEmptyList.of(1, 2, 3)
    val tail = list + listOf(100)
    println("${tail.contains(1)}")
    // true
    println("${tail.contains(100)}")
    // true
    Scala/Scalaz
    val list = NonEmptyList(1, 2, 3)
    val tail = list +: List(100)
    println(s"${tail.contains(1)}")
    // false
    println(s"${tail.contains(100)}")
    // treu
    ﾁｮｯﾄ違う…
    

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32. What is type?
    Kotlin/Arrow
    val list = NonEmptyList.of(1, 2, 3)
    val tail = list + listOf(100)
    println(tail)
    // ???
    println("${tail.contains(1)}")
    // true
    println("${tail.contains(100)}")
    // true
    Scala/Scalaz
    val list = NonEmptyList(1, 2, 3)
    val tail = list +: List(100)
    println(tail)
    // ???
    println(s"${tail.contains(1)}")
    // false
    println(s"${tail.contains(100)}")
    // treu
    tailの型は？
    

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33. What is type?
    Kotlin/Arrow
    val list = NonEmptyList.of(1, 2, 3)
    val tail = list + listOf(100)
    println(tail)
    // NonEmptyList(all=[1, 2, 3, 100])
    println("${tail.contains(1)}")
    // true
    println("${tail.contains(100)}")
    // true
    Scala/Scalaz
    val list = NonEmptyList(1, 2, 3)
    val tail = list +: List(100)
    println(tail)
    // List(NonEmpty[1,2,3], 100)
    println(s"${tail.contains(1)}")
    // false
    println(s"${tail.contains(100)}")
    // treu
    ListにCastされている
    

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34. Wrap-up
    - Scala and Kotlin have similer syntax
    - But inside is quite different
    - Take care with similer types (ex. List type design)
    - Check decompile code
    似てるけど中身は結構違う
    似ている型は挙動が同じか確認しよう
    デコンパイルしよう
    

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35. Thank you!
    Have a nice Scala & Kotlin!
    _kaelaela / Alp, Inc.
    

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