使用 uJson 库理解这个可变递归 Function

Question

I am trying to implement an insert function using the ujson library :

Here is my attempt:

import ujson.{Obj, Value}
import upickle.default._

object Example extends App {
  def r = transform(
    List(Map(
      "a" -> Map("b" -> Obj("c" -> List(1,2,3), "d" -> List(2,4,6))), 
      "e" -> Map("f" -> Obj("g" -> List(1,2,3)))))
  ).to(Value)

  def insert(j: ujson.Value, k: String, v: ujson.Value): Unit = j match {
    case a: ujson.Arr => a.arr.foreach(e => insert(e, k, v))
    case o: ujson.Obj =>
    if (o.obj.keySet contains k)  o.obj(k) = v
    else o.obj.values.foreach(e => insert(e, k, v))
    case _ => Nil
  }

  println(r)
  insert(r, "b", transform(None).to(Value))
  println(r)
}

However, this gives me output that is unchanged:

[{"a":{"b":{"c":[1,2,3],"d":[2,4,6]}},"e":{"f":{"g":[1,2,3]}}}]
[{"a":{"b":{"c":[1,2,3],"d":[2,4,6]}},"e":{"f":{"g":[1,2,3]}}}]

Given that the Value type is mutable, why does this not mutate and update the key, k, with value v for json value object r?

Answer 1

You are creating Value anew every time you call r so, every changes you would make to it, are dismissed.

You create one copy when you call println(r) .

Then you create a separate copy with insert(r, "b", transform(None).to(Value)) , mutate it and dismiss.

Then you are creating third copy with another println(r) .

If you want to refer to the same object use val instead of def .