Scala example source code file (History.scala)

This example Scala source code file (History.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

abstractiterable, evt, history, int, iterator, pub, queue, serializable, serialversionuid, subscriber

The History.scala Scala example source code

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



package scala
package collection
package mutable


/** `History[A, B]` objects may subscribe to events of
 *  type `A` published by an object of type `B`.
 *  The history subscriber object records all published events
 *  up to maximum number of `maxHistory` events.
 *
 *  @author  Matthias Zenger
 *  @version 1.0, 08/07/2003
 *  @since   1
 *
 *  @tparam Evt   Type of events.
 *  @tparam Pub   Type of publishers.
 */
@SerialVersionUID(5219213543849892588L)
class History[Evt, Pub]
extends AbstractIterable[(Pub, Evt)]
   with Subscriber[Evt, Pub]
   with Iterable[(Pub, Evt)]
   with Serializable
{
  protected val log: Queue[(Pub, Evt)] = new Queue
  val maxHistory: Int = 1000

  /** Notifies this listener with an event by enqueuing it in the log.
   *
   *  @param pub   the publisher.
   *  @param event the event.
   */
  def notify(pub: Pub, event: Evt) {
    if (log.length >= maxHistory)
      log.dequeue()

    log.enqueue((pub, event))
  }

  override def size: Int = log.length
  def iterator: Iterator[(Pub, Evt)] = log.iterator
  def events: Iterator[Evt] = log.iterator map (_._2)

  def clear() { log.clear() }

  /** Checks if two history objects are structurally identical.
   *
   *  @return true, iff both history objects contain the same sequence of elements.
   */
  override def equals(obj: Any): Boolean = obj match {
    case that: History[_, _] => this.log equals that.log
    case _                   => false
  }
  override def hashCode = log.hashCode()
}