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caarmen/kotlin-scala-cheat-sheet.md

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kotlin-scala-cheat-sheet.md
Language feature Kotlin Scala
Function 
fun triple(x: Int): Int {
    return x * 3
}
 
def triple(x: Int): Int = {
  x * 3
}
Single statement function 
fun triple(x: Int) = x * 3
 
def triple(x: Int) = x * 3
Immutable data class 
data class Name(
    val first: String,
    val last: String
)
 
case class Name(
                 first: String,
                 last: String
               )
Mutable data class 
data class Name(
    var first: String,
    var last: String
)
 
case class Name(
                 var first: String,
                 var last: String
               )
Enum 
enum class Day(val isFun: Boolean) {
    Monday(false),
    Tuesday(false),
    Wednesday(false),
    Thursday(false),
    Friday(false),
    Saturday(true),
    Sunday(true),
}
 
  enum Day(val isFun: Boolean):
    case Monday extends Day(false)
    case Tuesday extends Day(false)
    case Wednesday extends Day(false)
    case Thursday extends Day(false)
    case Friday extends Day(false)
    case Saturday extends Day(true)
    case Sunday extends Day(true)
Nullable (kotlin)/Option (scala) 
data class Name(
    val first: String,
    val middle: String?,
    val last: String
)

val shortName = Name(
    first = "John",
    middle = null,
    last = "Doe"
)

val fullName = Name(
    first = "Jane",
    middle = "Lynn",
    last = "Doe"
)

case class Name(
                 val first: String,
                 val middle: Option[String],
                 val last: String
               )

val shortName = Name(
  first = "John",
  middle = Option.empty,
  last = "Doe"
)

val fullName = Name(
  first = "Jane",
  middle = Option("Lynn"),
  last = "Doe"
)
Default parameter values 
data class Name(
    val first: String,
    val middle: String? = null,
    val last: String
)

val shortName = Name(
    first = "John",
    last = "Doe"
)

val fullName = Name(
    first = "Jane",
    middle = "Lynn",
    last = "Doe"
)

case class Name(
                 val first: String,
                 val middle: Option[String] = Option.empty,
                 val last: String
               )

val shortName = Name(
  first = "John",
  last = "Doe"
)

val fullName = Name(
  first = "Jane",
  middle = Option("Lynn"),
  last = "Doe"
)
Lambda 
fun tripleList(x: List<Int>) =
    x.map { item -> item * 3 }

fun tripleListImplicitParameter(x: List<Int>) =
    x.map { it * 3 }
 
def tripleList(x: List[Int]) =
  x.map(item => item * 3)

def tripleListImplicitParameter(x: List[Int]) =
  x.map(_ * 3)
when/match 
fun isSchoolNight(day: Day) = when (day) {
    Day.Sunday,
    Day.Monday,
    Day.Tuesday,
    Day.Wednesday,
    Day.Thursday -> true
    else -> false
}
 
def isSchoolNight(day: Day) = day match {
  case Day.Sunday |
       Day.Monday |
       Day.Tuesday |
       Day.Wednesday |
       Day.Thursday => true
  case _ => false
}
lazy val 
val foo: Foo by lazy {
    loadFoo()
}
 
lazy val foo: Foo = {
  loadFoo()
}
Extension function 
fun Int.triple() = this * 3
 
extension (x: Int) def triple() = {
  x * 3
}
Companion object 
class Foo {
    fun greet() = println(MESSAGE)
    companion object {
        private const val MESSAGE = "hello"
    }
}
 
class Foo {
  def greet() = println(Foo.MESSAGE)
}

object Foo {
  private final val MESSAGE = "hello"
}
Interfaces 
interface Greeter {
    fun greet()
}

class ConsoleGreeter() : Greeter {
    override fun greet() = println("Hello")
}
 
trait Greeter {
  def greet(): Unit
}

class ConsoleGreeter extends Greeter {
  override def greet() = println("Hello")
}
Range iteration 
val intRangeTripled: List<Int> =
    (0 until 5).map { it * 3 }
 
val intRangeTripled: List[Int] =
  (0 until 5).toList.map(_ * 3)
String template 
val displayName = "${name.first} ${name.last}"
 
val displayName = s"${name.first} ${name.last}"

Java interop:

Language feature Kotlin Scala
Java class 
val stringClass = String::class.java
 
val stringClass = classOf[String]
Convert from Java list 
fun tripleList(list: List<Int>) =
    list.map { it * 3 }
 
import scala.collection.JavaConverters.*

def tripleJavaListToScalaList(javaList: java.util.List[Int]): List[Int] =
  javaList.asScala.toList.map(_ * 3)
Convert to Java list 
fun tripleList(list: List<Int>) =
    list.map { it * 3 }
 
import scala.collection.JavaConverters.*

def tripleScalaListToJavaList(scalaList: List[Int]): java.util.List[Int] = 
  scalaList.map(_ * 3).asJava
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