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What a difference!
<-Scala & Kotlin->
@kaelaela
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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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Scala == Kotlin
???
ScalaとKotlinは同じ？
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Kotlin extends Scala
???
KotlinはScalaを真似して作られた？
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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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Kotlin philosophy / Kotlinの哲学
健全性よりも
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Scala != Kotlin
???
ScalaとKotlinは全然違う？
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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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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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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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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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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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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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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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How is Scala code decompiled?
public void main(final String[] args) {
User user = User$.MODULE$.apply("yuichi");
.MODULE$.println(user.name());
}
Scalaをデコンパイルするとシンプル
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How is Kotlin code decompiled?
public final class UserKt {
public static final void main() {
User var1 = new User((String)null, 1, (DefaultConstructorMarker)null);
~~~ // some variables by scope function
var1.setName("yuichi");
String var6 = var1.getName();
~~~
System.out.println(var6);
}
public static void main(String[] var0) { main(); }
}
Kotlinをデコンパイルすると？
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Top level function == ~~Kt class
public final class UserKt {
public static final void main() {
User var1 = new User((String)null, 1, (DefaultConstructorMarker)null);
~~~
var1.setName("yuichi");
String var6 = var1.getName();
~~~
System.out.println(var6);
}
public static void main(String[] var0) { main(); }
}
関数をトップにするとXXXKtクラスが自動生成
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How to show decompile code?(IntelliJ IDEA)
IDEAでデコンパイル
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How to show decompile code?(AS)
ASでデコンパイル
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Kotlin
fun main() {
val list = listOf(1)
when (list) {
is MutableList -> {
val add = list += 2
println("$add")
}
}
}
// ???
Scala
def main(args: ...): Unit = {
val list = MutableList(1)
list match {
case MutableList(_) => {
val add = list += 2
println(s"$add")
}
}
}
// ???
List
Kotlin puzzlers
https://github.com/angryziber/kotlin-puzzlers
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Kotlin
fun main() {
val list = listOf(1)
when (list) {
is MutableList -> {
val add = list += 2
println("$add")
}
}
}
// UnsupportedOperationException
Scala
def main(args: ...): Unit = {
val list = MutableList(1)
list match {
case MutableList(_) => {
val add = list += 2
println(s"$add")
}
}
}
// MutableList(1, 2)
List
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Kotlin
fun main() {
val list = listOf(1) // ArrayList!!!
when (list) {
is MutableList -> {
val add = list += 2
println("$add")
}
}
}
// UnsupportedOperationException
Scala
def main(args: ...): Unit = {
val list = MutableList(1)
list match {
case MutableList(_) => {
val add = list += 2
println(s"$add")
}
}
}
// MutableList(1, 2)
List
KotlinのlistOfはArrayList
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Kotlin cannot FP
???
Kotlinでは関数型ができないでしょうか
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Arrow
> Functional companion to Kotlin's Standard Library
Option
Either
Try
NonEmptyList
Validated
...
ArrowはKotlinの関数型実装をもつライブラリです
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Arrow
> Functional companion to Kotlin's Standard Library
Option
Either
Try
NonEmptyList
Validated
...
Default in Scala
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Arrow
> Functional companion to Kotlin's Standard Library
Option
Either
Try
NonEmptyList
Validated
...
Cats/Scalaz
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Arrow
> Functional companion to Kotlin's Standard Library
Option
Either
Try
NonEmptyList
Validated
...
Cats/Scalaz
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Scala/Cats
val list = NonEmptyList.of(1, 2, 3)
val tail = list ++ List(100)
println(s"${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("${tail.contains(100)}")
// ???
CatsとArrowの要素チェック
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The same results
Kotlin/Arrow
val list = NonEmptyList.of(1, 2, 3)
val tail = list + listOf(100)
println("${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"${tail.exists(_ == 100)}")
// true
結果は同じ
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Cats => Scalaz
Kotlin/Arrow
val list = NonEmptyList.of(1, 2, 3)
val tail = list + listOf(100)
println("${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"${tail.contains(100)}")
// ???
ScalazとArrow
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NOT the same results :-o
Kotlin/Arrow
val list = NonEmptyList.of(1, 2, 3)
val tail = list + listOf(100)
println("${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"${tail.contains(100)}")
// treu
ﾁｮｯﾄ違う…
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What is type?
Kotlin/Arrow
val list = NonEmptyList.of(1, 2, 3)
val tail = list + listOf(100)
println(tail)
// ???
println("${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"${tail.contains(100)}")
// treu
tailの型は？
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What is type?
Kotlin/Arrow
val list = NonEmptyList.of(1, 2, 3)
val tail = list + listOf(100)
println(tail)
// NonEmptyList(all=[1, 2, 3, 100])
println("${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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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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Thank you!
Have a nice Scala & Kotlin!
_kaelaela / Alp, Inc.