Scala example source code file (Publisher.scala)

This example Scala source code file (Publisher.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, evt, filter, hashmap, multimap, pub, publisher, set, sub, subscriber

The Publisher.scala Scala example source code

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



package scala
package collection
package mutable


/** `Publisher[A,This]` objects publish events of type `A`
 *  to all registered subscribers. When subscribing, a subscriber may specify
 *  a filter which can be used to constrain the number of events sent to the
 *  subscriber. Subscribers may suspend their subscription, or reactivate a
 *  suspended subscription. Class `Publisher` is typically used
 *  as a mixin. The abstract type `Pub` models the type of the publisher itself.
 *
 *  @tparam Evt      type of the published event.
 *
 *  @author  Matthias Zenger
 *  @author  Martin Odersky
 *  @version 2.8
 *  @since   1
 */
trait Publisher[Evt] {

  type Pub <: Publisher[Evt]
  type Sub = Subscriber[Evt, Pub]
  type Filter = Evt => Boolean

  /** The publisher itself of type `Pub`. Implemented by a cast from `this` here.
   *  Needs to be overridden if the actual publisher is different from `this`.
   */
  protected val self: Pub = this.asInstanceOf[Pub]

  private val filters = new HashMap[Sub, Set[Filter]] with MultiMap[Sub, Filter]
  private val suspended = new HashSet[Sub]

  def subscribe(sub: Sub) { subscribe(sub, event => true) }
  def subscribe(sub: Sub, filter: Filter) { filters.addBinding(sub, filter) }
  def suspendSubscription(sub: Sub) { suspended += sub }
  def activateSubscription(sub: Sub) { suspended -= sub }
  def removeSubscription(sub: Sub) { filters -= sub }
  def removeSubscriptions() { filters.clear() }

  protected def publish(event: Evt) {
    filters.keys.foreach(sub =>
      if (!suspended.contains(sub) &&
          filters.entryExists(sub, p => p(event)))
        sub.notify(self, event)
    )
  }

  /** Checks if two publishers are structurally identical.
   *
   *  @return true, iff both publishers contain the same sequence of elements.
   */
  override def equals(obj: Any): Boolean = obj match {
    case that: Publisher[_] => filters == that.filters && suspended == that.suspended
    case _                  => false
  }
}