<?php
  /*
   *  $Id$
   *
   * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
   * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
   * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
   * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
   * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
   * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
   * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
   * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
   * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
   * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
   * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
   *
   * This software consists of voluntary contributions made by many individuals
   * and is licensed under the MIT license. For more information, see
   * <http://www.doctrine-project.org>.
   */
  
  namespace Doctrine\Common;
  
  /**
   * EventArgs is the base class for classes containing event data.
   *
   * This class contains no event data. It is used by events that do not pass state
   * information to an event handler when an event is raised. The single empty EventArgs
   * instance can be obtained through {@link getEmptyInstance}.
   *
   * @license http://www.opensource.org/licenses/lgpl-license.php LGPL
   * @link    www.doctrine-project.org
   * @since   2.0
   * @version $Revision: 3938 $
   * @author  Guilherme Blanco <guilhermeblanco@hotmail.com>
   * @author  Jonathan Wage <jonwage@gmail.com>
   * @author  Roman Borschel <roman@code-factory.org>
   */
  class EventArgs
  {
      /**
       * @var EventArgs Single instance of EventArgs
       */
      private static $_emptyEventArgsInstance;
  
      /**
       * Gets the single, empty and immutable EventArgs instance.
       *
       * This instance will be used when events are dispatched without any parameter,
       * like this: EventManager::dispatchEvent('eventname');
       *
       * The benefit from this is that only one empty instance is instantiated and shared
       * (otherwise there would be instances for every dispatched in the abovementioned form)
       *
       * @see EventManager::dispatchEvent
       * @link http://msdn.microsoft.com/en-us/library/system.eventargs.aspx
       * @return EventArgs
       */
      public static function getEmptyInstance()
      {
          if ( ! self::$_emptyEventArgsInstance) {
              self::$_emptyEventArgsInstance = new EventArgs;
          }
  
          return self::$_emptyEventArgsInstance;
      }
  }