Kotlin generic constraint with "any of" rather than "all of"

Question

Question: Is there a way to constraint a generic type in Kotlin in a way that it can be a disjunction of a list of types, or "whatever has function foo", rather than a conjunction of the constraints?

where T:Type1, T:Type2<Foo>

means that T must comply with Type1 and Type2

But what if, for example, I want to extend Math with sqr, that operates on built in numeric types:

fun <T> Math.sqr(op:T): T 
    where T:Int or Long or Float or Double = op * op

or even on anything that has * or times:

fun <T> Math.sqr(op:T): T
    where T: can do times // like "responds to selector" in Obj-C
    = op.times(op)

Anything like that? The latter is cooler because T can be a "Complex" or vectors with "*" defined as their inner product... just imagine and implement.

Theoretically, I could have invented a set of "primitives" that inherit from "Math-able" but that's quite ugly because it means I need to use my own set of vars.

interface Mathable {
    fun plus(m:Mathable)
    fun minus(m:Mathable)
    fun times(m:Mathable)
    fun div(m:Mathable)
}

class Int2 : Number, Comparable<Int2>, Mathable

It's just as ugly (relatively speaking, of course...) as

inline fun <reified T:Number> sqr(n:T):T {
    return where n {
        is Int -> n * n
        is Float -> n * n
        is Whatever -> n * n
        ....
        else -> throw SomeException("huh?!")
    }
}

Is there a better/cooler way?

Update: Checking the Kotlin class Int code, makes me doubt. They just did it with overloading. Still, nice to know if that's possible.

Thanks

Answer 1

Unfortunately, the answer is:

1. No, currently there isn't.

2. Type classes proposal (or something similar) will fix it, if accepted (something like Mathable will be a type class).

3. even on anything that has * or times

   This is called structural types and I don't think anything similar is planned for Kotlin.