Kotlin and Upper type estimates with covariance

Question

Does Kotlin support upper and lower type constraints in setting covariance. For example, I want to say

class Foo<out T> { fun or<U of T or greater>(other: U): <U> = ... } 

which in Scala would be

 class Foo[+T] { def or[U >: T](other: U): U = ... } 

But the compiler does not seem to like this, he complains about the covariance of a parameter of type T.

Answer 1

Kotlin does not support lower ratings at this point. Sometimes you can get away with defining an extension function instead of a member:

 fun <T> Foo<T>.or(other: T): T = ...