EnumExt.kt

interface HasX {
    val x: Int

    companion object
}

enum class A(override val x: Int) : HasX { ONE(1), TWO(2) }
enum class B(override val x: Int, val w: String) : HasX { AB(2, "ab"), CDE(3, "cde") }


inline fun <reified T> KClass<T>.findX(x: Int): T? where T : HasX, T : Enum<T> {
    return enumValues<T>().find { it.x == x }
}

inline fun <reified T> findXOfEnum(x: Int): T? where T : HasX, T : Enum<T> {
    return enumValues<T>().find { it.x == x }
}

inline fun <reified T> HasX.Companion.findXOfEnum(x: Int): T? where T : HasX, T : Enum<T> {
    return enumValues<T>().find { it.x == x }
}

fun foo() {
    val classA = A::class.findX(2)

    val a = findXOfEnum<A>(2)
    val b = findXOfEnum<B>(3)

    val hax = HasX.findXOfEnum<A>(1)
}