Котлин запечатанные классы
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")
}
SAMER SAEID