Scala example source code file (LinearSeqLike.scala)

This example Scala source code file (LinearSeqLike.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, a,b, abstractiterator, annotation, boolean, iterablelike, iterator, linearseq, linearseqlike, list, repr

The LinearSeqLike.scala Scala example source code

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

package scala
package collection

import immutable.List
import scala.annotation.tailrec

/** A template trait for linear sequences of type `LinearSeq[A]`.
 *
 *  $linearSeqInfo
 *
 *  This trait just implements `iterator` in terms of `isEmpty, ``head`, and `tail`.
 *  However, see `LinearSeqOptimized` for an implementation trait that overrides operations
 *  to make them run faster under the assumption of fast linear access with `head` and `tail`.
 *
 *  @define  linearSeqInfo
 *  Linear sequences are defined in terms of three abstract methods, which are assumed
 *  to have efficient implementations. These are:
 *  {{{
 *     def isEmpty: Boolean
 *     def head: A
 *     def tail: Repr
 *  }}}
 *  Here, `A` is the type of the sequence elements and `Repr` is the type of the sequence itself.
 *
 *  Linear sequences do not add any new methods to `Seq`, but promise efficient implementations
 *  of linear access patterns.
 *  @author  Martin Odersky
 *  @version 2.8
 *  @since   2.8
 *
 *  @tparam A    the element type of the $coll
 *  @tparam Repr the type of the actual $coll containing the elements.
 */
trait LinearSeqLike[+A, +Repr <: LinearSeqLike[A, Repr]] extends SeqLike[A, Repr] {
  self: Repr =>

  override protected[this] def thisCollection: LinearSeq[A] = this.asInstanceOf[LinearSeq[A]]
  override protected[this] def toCollection(repr: Repr): LinearSeq[A] = repr.asInstanceOf[LinearSeq[A]]

  def seq: LinearSeq[A]

  override def hashCode()= scala.util.hashing.MurmurHash3.seqHash(seq) // TODO - can we get faster via "linearSeqHash" ?

  override /*IterableLike*/
  def iterator: Iterator[A] = new AbstractIterator[A] {
    var these = self
    def hasNext: Boolean = !these.isEmpty
    def next(): A =
      if (hasNext) {
        val result = these.head; these = these.tail; result
      } else Iterator.empty.next()

    /** Have to clear `these` so the iterator is exhausted like
     *  it would be without the optimization.
     */
    override def toList: List[A] = {
      val xs = these.toList
      these = newBuilder.result()
      xs
    }
  }

  @tailrec override final def corresponds[B](that: GenSeq[B])(p: (A,B) => Boolean): Boolean = {
    if (this.isEmpty) that.isEmpty
    else that.nonEmpty && p(head, that.head) && (tail corresponds that.tail)(p)
  }
}