Is there a way in Kotlin to create an empty EnumSet from a reflected enum Class? It seems like I can do it with Java, but not with Kotlin based on the enum type constraints and inference (and if I take Java code and paste it into Kotlin and have IntelliJ do the auto convert, it fails)

You can make use of generic type erasure, like this:

import java.util.EnumSet
import kotlin.reflect.KClass


private enum class Dummy


@Suppress("UNCHECKED_CAST")
fun <E: Enum<E>> emptyEnumSet(clazz: KClass<E>) =
	EnumSet.noneOf(clazz.java as Class<Dummy>) as EnumSet<E>


@JvmName("emptyEnumSetOfUnspecificClass")
@Suppress("UNCHECKED_CAST")
fun emptyEnumSet(clazz: KClass<out Enum<*>>) =
	EnumSet.noneOf(clazz.java as Class<Dummy>) as EnumSet<*>


@Suppress("UNCHECKED_CAST")
inline fun <reified E: Enum<E>> emptyEnumSet() =
	EnumSet.noneOf(E::class.java as Class<Dummy>) as EnumSet<E>


enum class MyEnum {
	a,b
}


fun main() {
	val unspecificEnumClass = MyEnum::class as KClass<out Enum<*>>
	val emptySet1 = emptyEnumSet(MyEnum::class)
	val emptySet2 = emptyEnumSet<MyEnum>()
	val emptySet3 = emptyEnumSet(unspecificEnumClass)

	println(emptySet1)
	println(emptySet2)
	println(emptySet3)
}

Thanks. The above didn't exactly work for my needs (because I'm dealing with a Class<?> coming from Java so type inference still wasn't happy, but the idea to create an empty enum class and then cast to that does seem to work, which I hadn't thought of before.

You can use the method above, again with a little cast:

val veryUnspecificClass: Class<*> = unspecificEnumClass.java
val emptySet4 = emptyEnumSet(veryUnspecificClass.kotlin as KClass<out Enum<*>>)

Yeah, I'm dealing with reflection, so I've already verified the class is an enum, so for my case it's safe

You can, I just generalized your use-case with some functions and added different examples. But you have to cast the resulting

EnumSet<Dummy>

to

EnumSet<*>

🙂

Cool. Yeah, in my case the value I'm assuming to is already Any?, so for me the cast isn't necessary

So could also be interesting for my own Kotlin JSON library 😄 I've never ever used

EnumSet

though 😮 Maybe I should add a Kotlin-version of it 🙂