[Changing the code] It's kotlin. How do I modify this code?

class Snapshot<T>(private val array: MutableList<T>) {
    var deepCopyArray:MutableList<T> = ArrayList()

    init {
        deepCopyArray.addAll(array)
    }

    fun restore():MutableList<T> {
        array.clear()
        array.addAll(deepCopyArray)
        return array
    }
}
fun test2(){
    var array = mutableListOf(1,2)
    val snap = Snapshot(array)
    array[0] = 1
    array = snap.restore()
    println(array.toList().joinToString()) //It should log "1,2"
    array.add(4)
    array = snap.restore()
    println(array.toList().joinToString()) //It should log "1,2"
}

fun main(str: Array<String>) {
    test2()
}

//Current state output:
1, 2
1, 2

//Normal output:
1, 2
1, 2