Deep copy and partial changes

Basically I like the idea how Kotlin does provide readonly / immutable classes
but I would like to know how elegant it’s possible to solve following problem:

Considering following:

data class Node(val title: String, val subNodes: List<Node> = emptyList())

now writing 

val root = Node("root  node", listOf(
    Node("child one"), Node("child two", listOf(
        Node("child two one"), Node("child two two")

 a) will "root.copy()" be a deep copy?
 b) how can I get a copy of the hierarchy with node "child two two" changed (adding a child node "child three")

 Recursion? Can the data class copy function be nicely interfaced?


No, copy is shallow. It’s just property assignments that are overridable.

What you want are commonly referred to as lenses (deep immutable object changes). Arrow has them.