E.g. why does

val list:List[Any] = List[Int](1,2,3)
work, but

val arr:Array[Any] = Array[Int](1,2,3)
fails (because arrays are invariant). What is the desired effect behind this design decision?

import scala.collection.mutable
object Main {
   case class Node(id: String, children: Seq[Node])
   def tail(ids: String*): Seq[Node] = ids.map(id => Node(id, Nil))
   def node(id: String, children: Seq[Node] = Nil): Node = Node(id, children)

   def main(args: Array[String]): Unit = {
       println("hello, world!")
       test(node("a"))
       test(node("a", tail("a1", "a2")))
       test(node("a", Seq(node("a1", tail("a2")))))
       test(node("a", Seq(node("a1", tail("a11", "a12")), node("a2", tail("a21", "a22", "a23")))))
   }

   def test(n: Node) = {
       val s = serialize(n)
       println(s)
       val ds = deserialize(serialize(n))
       println(ds)
       println(s == serialize(ds) && ds == n)
   }

   def serialize(n: Node): String = {
       val sb = new mutable.StringBuilder
       doSerialize(n, sb)
       val s = sb.toString
       s.lastIndexWhere(_ != ',') match {
           case -1 => s
           case i => s.substring(0, i + 1)
       }
   }

   def doSerialize(n:…