src/library/scala/collection/parallel/mutable/LazyCombiner.scala


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package scala.collection.parallel.mutable


import scala.collection.generic.Growable
import scala.collection.generic.Sizing
import scala.collection.mutable.ArrayBuffer
import scala.collection.parallel.Combiner


/** Implements combining contents of two combiners
 *  by postponing the operation until `result` method is called. It chains
 *  the leaf results together instead of evaluating the actual collection.
 *
 *  @tparam Elem    the type of the elements in the combiner
 *  @tparam To      the type of the collection the combiner produces
 *  @tparam Buff    the type of the buffers that contain leaf results and this combiner chains together
 */
trait LazyCombiner[Elem, +To, Buff <: Growable[Elem] with Sizing] extends Combiner[Elem, To]
{
self: collection.parallel.EnvironmentPassingCombiner[Elem, To] =>
  val chain: ArrayBuffer[Buff]
  val lastbuff = chain.last
  def +=(elem: Elem) = { lastbuff += elem; this }
  def result: To = allocateAndCopy
  def clear = { chain.clear }
  def combine[N <: Elem, NewTo >: To](other: Combiner[N, NewTo]): Combiner[N, NewTo] = if (this ne other) {
    if (other.isInstanceOf[LazyCombiner[_, _, _]]) {
      val that = other.asInstanceOf[LazyCombiner[Elem, To, Buff]]
      newLazyCombiner(chain ++= that.chain)
    } else throw new UnsupportedOperationException("Cannot combine with combiner of different type.")
  } else this
  def size = chain.foldLeft(0)(_ + _.size)

  /** Method that allocates the data structure and copies elements into it using
   *  `size` and `chain` members.
   */
  def allocateAndCopy: To
  def newLazyCombiner(buffchain: ArrayBuffer[Buff]): LazyCombiner[Elem, To, Buff]
}