Given a `reified R` I would like to return a default comparator to use based on `R`s type Is there any way to do something like this ``` inline fun lt reified R gt defaultComparator Comparator lt R gt = when R class isSubclassOf Comparable class gt naturalOrder lt R gt Error Type arg not within bounds others else gt null ```

`naturalOrder` expects a `Comparable lt R gt ` but AFAIK there s no way to indicate that `R` is `Comparable lt R gt `

`naturalOrder lt Nothing gt as Comparator lt R gt `

Or you could bound R to Comparable lt R gt if you want to operate only on comparable types

Can t do that unfortunately it s possible `R` is not `Comparable lt R gt `

Given a `reified R` I would like to return a default compara kotlinlang #announcements

11/29/2018, 1:44 PM

reified R

I would like to return a default comparator to use based on `R`s type. Is there any way to do something like this?

inline fun <reified R> defaultComparator(): Comparator<R>? = when {
    R::class.isSubclassOf(Comparable::class) -> naturalOrder<R>()  // Error: Type arg not within bounds
    // ... others
    else -> null
}

11/29/2018, 1:47 PM

You'll have to do an unchecked cast here

11/29/2018, 1:51 PM

naturalOrder

Comparable<R>

but AFAIK there's no way to indicate that

Comparable<R>

11/29/2018, 1:53 PM

naturalOrder<Nothing>() as Comparator<R>

11/29/2018, 1:58 PM

Thanks! Never would have thought to try that

11/29/2018, 1:59 PM

Nothing

is a great tool if you're trying to fight the type system 😄

Katya Yurukova

11/29/2018, 2:04 PM

Or you could bound R to Comparable<R> if you want to operate only on comparable types

11/29/2018, 4:04 PM

Can't do that unfortunately, it's possible

Comparable<R>