A simple code challenge

flattenArrays.kt

// Feel free to run it here try.kotlinlang.org

fun main(args: Array<String>) {
    val testCollection = arrayOf(
            1, 2, 3,
            arrayOf(4, 5, emptyArray<Int>()), null,
            arrayOf(emptyArray<Int>(), emptyArray<Int>()),
            arrayOf(6)
    )

    System.out.println("Collection:")
    testCollection.forEach { System.out.print("$it ") } // The JVM doesn't print Lists the same way than Arrays

    System.out.println("Result:")
    testCollection.flattenArray().forEach { System.out.print("$it ") }
}

fun <T: Any?> Array<T>.flattenArray(): Array<*> {
    // Easier to handle a mutable list than an array
    val flatList = mutableListOf<Any?>()
    flattenArray(this, flatList)
    return flatList.toTypedArray()
}

private fun <T: Any?> Array<T>.flattenArray(nestedList: Array<*>, flatList: MutableList<Any?>) {
    nestedList.forEach{
        e -> when(e){
            !is Array<*> -> flatList.add(e)
            else -> flattenArray(e, flatList)
        }
    }
}