Scala example source code file (Combiner.scala)

This example Scala source code file (Combiner.scala) is included in my "Source Code Warehouse" project. The intent of this project is to help you more easily find Scala source code examples by using tags.

All credit for the original source code belongs to scala-lang.org; I'm just trying to make examples easier to find. (For my Scala work, see my Scala examples and tutorials.)

Scala tags/keywords

boolean, builder, collection, combiner, elem, generics, mutable, newto, parallel, sizing, tasksupport, to

The Combiner.scala Scala example source code

/*                     __                                               *\
**     ________ ___   / /  ___     Scala API                            **
**    / __/ __// _ | / /  / _ |    (c) 2003-2013, LAMP/EPFL             **
**  __\ \/ /__/ __ |/ /__/ __ |    http://scala-lang.org/               **
** /____/\___/_/ |_/____/_/ | |                                         **
**                          |/                                          **
\*                                                                      */

package scala
package collection.parallel

import scala.collection.Parallel
import scala.collection.mutable.Builder
import scala.collection.generic.Sizing

/** The base trait for all combiners.
 *  A combiner incremental collection construction just like
 *  a regular builder, but also implements an efficient merge operation of two builders
 *  via `combine` method. Once the collection is constructed, it may be obtained by invoking
 *  the `result` method.
 *
 *  The complexity of the `combine` method should be less than linear for best
 *  performance. The `result` method doesn't have to be a constant time operation,
 *  but may be performed in parallel.
 *
 *  @tparam Elem   the type of the elements added to the builder
 *  @tparam To     the type of the collection the builder produces
 *
 *  @author Aleksandar Prokopec
 *  @since 2.9
 */
trait Combiner[-Elem, +To] extends Builder[Elem, To] with Sizing with Parallel {

  @transient
  @volatile
  var _combinerTaskSupport = defaultTaskSupport

  def combinerTaskSupport = {
    val cts = _combinerTaskSupport
    if (cts eq null) {
      _combinerTaskSupport = defaultTaskSupport
      defaultTaskSupport
    } else cts
  }

  def combinerTaskSupport_=(cts: TaskSupport) = _combinerTaskSupport = cts

  /** Combines the contents of the receiver builder and the `other` builder,
   *  producing a new builder containing both their elements.
   *
   *  This method may combine the two builders by copying them into a larger collection,
   *  by producing a lazy view that gets evaluated once `result` is invoked, or use
   *  a merge operation specific to the data structure in question.
   *
   *  Note that both the receiver builder and `other` builder become invalidated
   *  after the invocation of this method, and should be cleared (see `clear`)
   *  if they are to be used again.
   *
   *  Also, combining two combiners `c1` and `c2` for which `c1 eq c2` is `true`, that is,
   *  they are the same objects in memory:
   *
   *  {{{
   *  c1.combine(c2)
   *  }}}
   *
   *  always does nothing and returns `c1`.
   *
   *  @tparam N      the type of elements contained by the `other` builder
   *  @tparam NewTo  the type of collection produced by the `other` builder
   *  @param other   the other builder
   *  @return        the parallel builder containing both the elements of this and the `other` builder
   */
  def combine[N <: Elem, NewTo >: To](other: Combiner[N, NewTo]): Combiner[N, NewTo]

  /** Returns `true` if this combiner has a thread-safe `+=` and is meant to be shared
   *  across several threads constructing the collection.
   *
   *  By default, this method returns `false`.
   */
  def canBeShared: Boolean = false

  /** Constructs the result and sets the appropriate tasksupport object to the resulting collection
   *  if this is applicable.
   */
  def resultWithTaskSupport: To = {
    val res = result()
    setTaskSupport(res, combinerTaskSupport)
  }
}

/*
private[collection] trait EnvironmentPassingCombiner[-Elem, +To] extends Combiner[Elem, To] {
  abstract override def result = {
    val res = super.result
    res
  }
}
*/