Scala example source code file (IterableViewLike.scala)

This example Scala source code file (IterableViewLike.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

a, a1, abstracttransformed, b, geniterable, int, iterator, that, this, transformed

The IterableViewLike.scala Scala example source code

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

package scala
package collection

import generic._
import immutable.Stream
import scala.language.implicitConversions

/** A template trait for non-strict views of iterable collections.
 *  $iterableViewInfo
 *
 *  @define iterableViewInfo
 *  $viewInfo
 *  All views for iterable collections are defined by re-interpreting the `iterator` method.
 *
 *  @author Martin Odersky
 *  @version 2.8
 *  @since   2.8
 *  @tparam A    the element type of the view
 *  @tparam Coll the type of the underlying collection containing the elements.
 *  @tparam This the type of the view itself
 */
trait IterableViewLike[+A,
                       +Coll,
                       +This <: IterableView[A, Coll] with IterableViewLike[A, Coll, This]]
     extends Iterable[A]
        with IterableLike[A, This]
        with TraversableView[A, Coll]
        with TraversableViewLike[A, Coll, This]
{ self =>

  /** Explicit instantiation of the `Transformed` trait to reduce class file size in subclasses. */
  private[collection] abstract class AbstractTransformed[+B] extends Iterable[B] with super[TraversableViewLike].Transformed[B] with Transformed[B]

  trait Transformed[+B] extends IterableView[B, Coll] with super.Transformed[B] {
    def iterator: Iterator[B]
    override def foreach[U](f: B => U): Unit = iterator foreach f
    override def toString = viewToString
    override def isEmpty = !iterator.hasNext
  }

  trait EmptyView extends Transformed[Nothing] with super.EmptyView {
    final def iterator: Iterator[Nothing] = Iterator.empty
  }

  trait Forced[B] extends super.Forced[B] with Transformed[B] {
    def iterator = forced.iterator
  }

  trait Sliced extends super.Sliced with Transformed[A] {
    def iterator: Iterator[A] = self.iterator.slice(from, until)
  }

  trait Mapped[B] extends super.Mapped[B] with Transformed[B] {
    def iterator = self.iterator map mapping
  }

  trait FlatMapped[B] extends super.FlatMapped[B] with Transformed[B] {
    def iterator: Iterator[B] = self.iterator flatMap mapping
  }

  trait Appended[B >: A] extends super.Appended[B] with Transformed[B] {
    def iterator = self.iterator ++ rest
  }

  trait Filtered extends super.Filtered with Transformed[A] {
    def iterator = self.iterator filter pred
  }

  trait TakenWhile extends super.TakenWhile with Transformed[A] {
    def iterator = self.iterator takeWhile pred
  }

  trait DroppedWhile extends super.DroppedWhile with Transformed[A] {
    def iterator = self.iterator dropWhile pred
  }

  trait Zipped[B] extends Transformed[(A, B)] {
    protected[this] val other: GenIterable[B]
    def iterator: Iterator[(A, B)] = self.iterator zip other.iterator
    final override protected[this] def viewIdentifier = "Z"
  }

  trait ZippedAll[A1 >: A, B] extends Transformed[(A1, B)] {
    protected[this] val other: GenIterable[B]
    protected[this] val thisElem: A1
    protected[this] val thatElem: B
    final override protected[this] def viewIdentifier = "Z"
    def iterator: Iterator[(A1, B)] =
      self.iterator.zipAll(other.iterator, thisElem, thatElem)
  }

  private[this] implicit def asThis(xs: Transformed[A]): This = xs.asInstanceOf[This]

  /** Boilerplate method, to override in each subclass
   *  This method could be eliminated if Scala had virtual classes
   */
  protected def newZipped[B](that: GenIterable[B]): Transformed[(A, B)] = new { val other = that } with AbstractTransformed[(A, B)] with Zipped[B]
  protected def newZippedAll[A1 >: A, B](that: GenIterable[B], _thisElem: A1, _thatElem: B): Transformed[(A1, B)] = new {
    val other: GenIterable[B] = that
    val thisElem = _thisElem
    val thatElem = _thatElem
  } with AbstractTransformed[(A1, B)] with ZippedAll[A1, B]
  protected override def newForced[B](xs: => GenSeq[B]): Transformed[B] = new { val forced = xs } with AbstractTransformed[B] with Forced[B]
  protected override def newAppended[B >: A](that: GenTraversable[B]): Transformed[B] = new { val rest = that } with AbstractTransformed[B] with Appended[B]
  protected override def newMapped[B](f: A => B): Transformed[B] = new { val mapping = f } with AbstractTransformed[B] with Mapped[B]
  protected override def newFlatMapped[B](f: A => GenTraversableOnce[B]): Transformed[B] = new { val mapping = f } with AbstractTransformed[B] with FlatMapped[B]
  protected override def newFiltered(p: A => Boolean): Transformed[A] = new { val pred = p } with AbstractTransformed[A] with Filtered
  protected override def newSliced(_endpoints: SliceInterval): Transformed[A] = new { val endpoints = _endpoints } with AbstractTransformed[A] with Sliced
  protected override def newDroppedWhile(p: A => Boolean): Transformed[A] = new { val pred = p } with AbstractTransformed[A] with DroppedWhile
  protected override def newTakenWhile(p: A => Boolean): Transformed[A] = new { val pred = p } with AbstractTransformed[A] with TakenWhile

  // After adding take and drop overrides to IterableLike, these overrides (which do nothing
  // but duplicate the implementation in TraversableViewLike) had to be added to prevent the
  // overrides in IterableLike from besting the overrides in TraversableViewLike when mixed
  // together in e.g. SeqViewLike.  This is a suboptimal situation.  Examples of failing tests
  // are run/bug2876 and run/viewtest.
  protected override def newTaken(n: Int): Transformed[A] = newSliced(SliceInterval(0, n))
  protected override def newDropped(n: Int): Transformed[A] = newSliced(SliceInterval(n, Int.MaxValue))
  override def drop(n: Int): This = newDropped(n)
  override def take(n: Int): This = newTaken(n)

  override def zip[A1 >: A, B, That](that: GenIterable[B])(implicit bf: CanBuildFrom[This, (A1, B), That]): That = {
    newZipped(that).asInstanceOf[That]
// was:    val b = bf(repr)
//    if (b.isInstanceOf[NoBuilder[_]]) newZipped(that).asInstanceOf[That]
//    else super.zip[A1, B, That](that)(bf)
  }

  override def zipWithIndex[A1 >: A, That](implicit bf: CanBuildFrom[This, (A1, Int), That]): That =
    zip[A1, Int, That](Stream from 0)(bf)

  override def zipAll[B, A1 >: A, That](that: GenIterable[B], thisElem: A1, thatElem: B)(implicit bf: CanBuildFrom[This, (A1, B), That]): That =
    newZippedAll(that, thisElem, thatElem).asInstanceOf[That]

  override def grouped(size: Int): Iterator[This] =
    self.iterator grouped size map (x => newForced(x).asInstanceOf[This])

  override def sliding(size: Int, step: Int): Iterator[This] =
    self.iterator.sliding(size, step) map (x => newForced(x).asInstanceOf[This])

  override def sliding(size: Int): Iterator[This] =
    sliding(size, 1) // we could inherit this, but that implies knowledge of the way the super class is implemented.

  override def dropRight(n: Int): This =
    take(thisSeq.length - n)

  override def takeRight(n: Int): This =
    drop(thisSeq.length - n)

  override def stringPrefix = "IterableView"
}