JAVA

Kotlin Sealed Classes

class Expr
class Const(val value: Int) : Expr
class Sum(val left: Expr, val right: Expr) : Expr

fun eval(e: Expr): Int =
        when (e) {
            is Const -> e.value
            is Sum -> eval(e.right) + eval(e.left)
            else ->
                throw IllegalArgumentException("Unknown expression")
        }

sealed class in kotlin example

sealed interface Expr

sealed class MathExpr(): Expr

data class Const(val number: Double) : MathExpr()

data class Sum(val e1: Expr, val e2: Expr) : MathExpr()

object NotANumber : Expr

sealed class in kotlin example

sealed class Message {
    abstract val messageId: String
}
data class Track(val event: String, override val messageId: String): Message()

Kotlin Sealed Class

sealed class Expr
class Const(val value: Int) : Expr()
class Sum(val left: Expr, val right: Expr) : Expr()
object NotANumber : Expr()


fun eval(e: Expr): Int =
        when (e) {
            is Const -> e.value
            is Sum -> eval(e.right) + eval(e.left)
            NotANumber -> java.lang.Double.NaN
        }