path: root/src/library/scala/collection/mutable/ArrayStack.scala

/*                     __                                               *\
**     ________ ___   / /  ___     Scala API                            **
**    / __/ __// _ | / /  / _ |    (c) 2003-2009, LAMP/EPFL             **
**  __\ \/ /__/ __ |/ /__/ __ |    http://scala-lang.org/               **
** /____/\___/_/ |_/____/_/ | |                                         **
**                          |/                                          **
\*                                                                      */

// $Id$


package scala.collection.mutable

import scala.collection.generic._

private object Utils {
  def growArray(x: Array[AnyRef]) = {
    val y = new Array[AnyRef](x.length * 2)
    Array.copy(x, 0, y, 0, x.length)
    y
  }

  def clone(x: Array[AnyRef]) = {
    val y = new Array[AnyRef](x.length)
    Array.copy(x, 0, y, 0, x.length)
    y
  }
}

/**
 * Simple stack class backed by an array. Should be significantly faster
 * than the standard mutable stack.
 *
 * @author David MacIver
 */
@cloneable
class ArrayStack[T] private(private var table : Array[AnyRef],
                            private var index : Int) extends collection.Sequence[T] with Cloneable[ArrayStack[T]] {
  def this() = this(new Array[AnyRef](1), 0)

  /** Retrieve n'th element from stack, where top of stack has index 0 */
  def apply(n: Int): T =
    table(index - 1 - n).asInstanceOf[T]

  /** The number of elements in the stack */
  def length = index

  /**
   * Push an element onto the stack.
   *
   * @param x The element to push
   */
  def push(x: T) {
    if (index == table.length) table = Utils.growArray(table)
    table(index) = x.asInstanceOf[AnyRef]
    index += 1
  }

  /**
   * Pop the top element off the stack.
   */
  def pop: T = {
    if (index == 0) error("Stack empty")
    index -= 1
    val x = table(index).asInstanceOf[T]
    table(index) = null
    x
  }

  /** View the top element of the stack. */
  @deprecated("use top instead")
  def peek = top

  /**
   * View the top element of the stack.
   */
  def top: T = table(index - 1).asInstanceOf[T]

  /**
   * Duplicate the top element of the stack.
   */
  def dup = push(top)

  /**
   * Empties the stack.
   */
  def clear {
    index = 0
    table = new Array(1)
  }

  /**
   * Empties the stack, passing all elements on it in FIFO order to the
   * provided function.
   *
   * @param f The function to drain to.
   */
  def drain(f: T => Unit) = while (!isEmpty) f(pop)

  /**
   * Pushes all the provided elements onto the stack.
   *
   * @param x The source of elements to push
   */
  def ++=(x: collection.Iterable[T]): this.type = { x.foreach(this +=(_)); this }


  /**
   * Pushes all the provided elements onto the stack.
   *
   * @param x The source of elements to push
   */
  def ++=(x: Iterator[T]): this.type = { x.foreach(this +=(_)); this }

  /**
   *  Alias for push.
   *
   *  @param x The element to push
   */
  def +=(x: T): this.type = { push(x); this }

  /**
   * Pop the top two elements off the stack, apply f to them and push the result
   * back on to the stack.
   *
   * @param f The combining function
   */
  def combine(f: (T, T) => T) = push(f(pop, pop));

  /**
   * Repeatedly combine the top elements of the stack until the stack contains only
   * one element.
   */
  def reduceWith(f: (T, T) => T) = while(size > 1) combine(f)

  override def size = index

  /**
   * Evaluates the expression, preserving the contents of the stack so that
   * any changes the evaluation makes to the stack contents will be undone after
   * it completes.
   *
   * @param action The action to run.
   */
  def preserving[T](action: => T) = {
    val oldIndex = index
    val oldTable = Utils.clone(table)

    try {
      action
    } finally {
      index = oldIndex
      table = oldTable
    }
  }

  override def isEmpty: Boolean = index == 0

  /**
   * Iterates over the stack in LIFO order.
   */
  def iterator: Iterator[T] = new Iterator[T] {
    var currentIndex = index
    def hasNext = currentIndex > 0
    def next = {
      currentIndex -= 1
      table(currentIndex).asInstanceOf[T]
    }
  }

  override def foreach[U](f: T =>  U) {
    var currentIndex = index
    while (currentIndex > 0) {
      currentIndex -= 1
      f(table(currentIndex).asInstanceOf[T])
    }
  }

  override def clone = new ArrayStack[T](Utils.clone(table), index)
}