So.. is there any other solution ?

What do you want to achieve? Can you describe for those who does not know Scala?

vote for the following issue: https://youtrack.jetbrains.com/issue/KT-209 Kotlin does not support lower bounds yet

And there is a solution in a comment to this issue. Use extension function:

fun <B, A : B> Test<A>.test(): B

@Pavlo Liapota I want to implement the class like with Scala’s Option. And I’m confused to implement to getOrElse function. It takes a type

[B >: A]

which means the type B is supertype of A. How can I implement this code to kotlin???

sealed abstract class Option[+A] extends Product with Serializable {
  self =>

    ... 
  @inline final def getOrElse[B >: A](default: => B): B =
    if (isEmpty) default else this.get
    ...

Thx!