ummutable.scala

import scala.collection.mutable.ListBuffer

class Ummutable[T] private (buf: ListBuffer[T]) {
  def this(xs: T*) = this(ListBuffer() ++= xs)
  def append(ys: T*): this.type = { buf ++= ys ; this }

  val xs: List[T] = buf.toIterable match { case xs: List[T] => xs }
  override def toString = s"Ummutable(xs = ${xs mkString ", "})"
}

object Ummm {
  def main(args: Array[String]): Unit = {
    val um = new Ummutable(1, 2, 3)
    println("um: " + um.xs)
    um append (4, 5, 6)
    println("um: " + um.xs)
  }
  // um: List(1, 2, 3)
  // um: List(1, 2, 3, 4, 5, 6)
}