varargs.scala

package policy

import scala.reflect.ClassTag

trait Iterator[@specialized +A] extends scala.Iterator[A] {
  def next(): A
  def hasNext: Boolean
}
object Iterator {
  def wrap[A](it: scala.Iterator[A]): Iterator[A] = new Iterator[A] {
    def next(): A = it.next
    def hasNext   = it.hasNext
  }
}

trait Varargs[@specialized +A] {
  def toArray: Array[Any]
  def seq: Seq[A]
  def length: Int
  def apply(idx: Int): A
  def foreach(f: A => Unit): Unit = iterator foreach f
  def iterator: Iterator[A]       = Iterator wrap seq.iterator
}

object Varargs {
  final val emptyArray: Array[Any] = new Array[Any](0)

  implicit def unwrapVarargs[A](xs: Varargs[A]): Seq[A]                = xs.seq
  implicit def wrapVarargs[A](xs: scala.collection.Seq[A]): Varargs[A] = new VarargsSeq[A](xs)

  def toScala[A](): Varargs[A]                            = EmptyVarargs
  def toScala[A](xs: Varargs[A]): Varargs[A]              = xs
  def toScala[A](xs: Array[A]): Varargs[A]                = new VarargsArray(xs)
  def toScala[A](xs: scala.collection.Seq[A]): Varargs[A] = new VarargsSeq(xs)

  def toJava[A](): Array[Any]                            = emptyArray
  def toJava[A](xs: Varargs[A]): Array[Any]              = xs.toArray
  def toJava[A](xs: Array[A]): Array[Any]                = xs.asInstanceOf[Array[Any]]
  def toJava[A](xs: scala.collection.Seq[A]): Array[Any] = xs.toArray[Any]
}

final object EmptyVarargs extends Varargs[Nothing] {
  def toArray                  = Varargs.emptyArray
  def seq                      = Nil
  def apply(idx: Int): Nothing = sys error "empty.apply"
  def length: Int              = 0
}
final class VarargsArray[@specialized +A](xs: Array[A]) extends Varargs[A] {
  def toArray                      = xs.asInstanceOf[Array[Any]]
  def seq: scala.collection.Seq[A] = xs
  def apply(idx: Int): A           = seq(idx)
  def length: Int                  = seq.length
}
final class VarargsSeq[+A](xs: scala.collection.Seq[A]) extends Varargs[A] {
  def toArray            = xs.toArray[Any]
  def seq                = xs
  def apply(idx: Int): A = xs(idx)
  def length: Int        = xs.length
}