How to change return type for getter in Kotlin?

Question

Kotlin

class Order(iitems: List<OrderItem>) {
    private val items: MutableList<OrderItem> = items.toMutableList()
}

Take an immutable OrderItem list as input, store it as mutable, and return the value as immutable.
Does not work:

class Order(items: List<OrderItem>) {
    private val items: MutableList<OrderItem> = items.toMutableList()
        get():List<OrderItem> = field.toList()
}

The language does not allow you to change the return type for a getter. With an error (Getter return type must be equal to the type of the property.)
I get around this problem as follows:

class Order(items: List<OrderItem>) {
    private val _items: MutableList<OrderItem> = items.toMutableList()

    val items: List<OrderItem>
        get() = _items.toList()
}

The code works, but Kotlin is getting verbose. Is there a way to more elegantly implement what was intended? It is possible through the classical method using simple methods, but I want to keep the style of direct access to the fields.

Answer 1

Normal code. Unless .toList() can be removed.
In Kotlin version 1.4, it will be possible to use delegation by property:
val items: List<OrderItem> by this::_items

Answer 2

The code works, but Kotlin seems to get verbose in this scenario.

Why such a bike? You can pass a MutableList to the constructor right away, and when the field is called from outside, convert it back to a List.