Set seed of XorWowRandom in Kotlin.

RandomExt.kt

import kotlin.random.Random
import kotlin.reflect.full.declaredMemberProperties
import kotlin.reflect.jvm.isAccessible

fun main() {
   val random = Random(42)
    println(random.nextInt())
    println(random.nextInt())
    println(random.nextInt())
    println(random.nextInt())
    random.setSeed(42)
    println(random.nextInt())
    println(random.nextInt())
    println(random.nextInt())
    println(random.nextInt())
}

fun Random.setSeed(seed: Int) {
    if (this::class.qualifiedName != "kotlin.random.XorWowRandom") {
        throw IllegalArgumentException("This method only works with XorWowRandom")
    }

    val seed1 = seed
    val seed2 = seed.shr(31)

    this::class.declaredMemberProperties.forEach { prop ->
        prop.isAccessible = true
        when (prop.name) {
            "x" -> (prop as kotlin.reflect.KMutableProperty<*>).setter.call(this, seed1)
            "y" -> (prop as kotlin.reflect.KMutableProperty<*>).setter.call(this, seed2)
            "z" -> (prop as kotlin.reflect.KMutableProperty<*>).setter.call(this, 0)
            "w" -> (prop as kotlin.reflect.KMutableProperty<*>).setter.call(this, 0)
            "v" -> (prop as kotlin.reflect.KMutableProperty<*>).setter.call(this, seed1.inv())
            "addend" -> (prop as kotlin.reflect.KMutableProperty<*>).setter.call(this, (seed1 shl 10) xor (seed2 ushr 4))
        }
    }

    // Discard first 64 values as done in the original constructor
    repeat(64) { this.nextInt() }
}

fun Random.setSeed(seed: Long) {
    if (this::class.qualifiedName != "kotlin.random.XorWowRandom") {
        throw IllegalArgumentException("This method only works with XorWowRandom")
    }

    val seed1 = seed.toInt()
    val seed2 = seed.shr(32).toInt()

    this::class.declaredMemberProperties.forEach { prop ->
        prop.isAccessible = true
        when (prop.name) {
            "x" -> (prop as kotlin.reflect.KMutableProperty<*>).setter.call(this, seed1)
            "y" -> (prop as kotlin.reflect.KMutableProperty<*>).setter.call(this, seed2)
            "z" -> (prop as kotlin.reflect.KMutableProperty<*>).setter.call(this, 0)
            "w" -> (prop as kotlin.reflect.KMutableProperty<*>).setter.call(this, 0)
            "v" -> (prop as kotlin.reflect.KMutableProperty<*>).setter.call(this, seed1.inv())
            "addend" -> (prop as kotlin.reflect.KMutableProperty<*>).setter.call(this, (seed1 shl 10) xor (seed2 ushr 4))
        }
    }

    // Discard first 64 values as done in the original constructor
    repeat(64) { this.nextInt() }
}