How can I write “this function accepts a parameter that should implement both Comparable and Serializable” (or any other two interfaces). I know I can define a generic as

<T: out Comparable>

to get the first one, but I don't see how to have two constraints.

you can use

where

(https://kotlinlang.org/docs/reference/generics.html#upper-bounds) e.g.

fun <T> test(t: T) where T : Comparable<T>, T : Serializable

Wow, that's amazing, thanks!