Kotlin - Most idiomatic way to convert a List to a MutableList

Consider using the toMutableList() function:

presenter.getContacts().toMutableList()

There are toMutableList() extensions for the stdlib types that one might want to convert to a mutable list: Collection<T>, Iterable<T>, Sequence<T>, CharSequence, Array<T> and primitive arrays.

If you only wants ArrayList, you can create your own Kotlin extension.

fun <T> List<T>.toArrayList(): ArrayList<T>{
    return ArrayList(this)
}

Then you can use it in your application like

myList.toArrayList()

Simple and easy