root/trunk/system/libraries/Event_Observer.php

<?php
/**
 * Kohana event observer. Uses the SPL observer pattern.
 *
 * $Id$
 *
 * @package    Core
 * @author     Kohana Team
 * @copyright  (c) 2007-2008 Kohana Team
 * @license    http://kohanaphp.com/license.html
 */
abstract class Event_Observer implements SplObserver {

    // Calling object
    protected $caller;

    /**
     * Initializes a new observer and attaches the subject as the caller.
     *
     * @param   object  Event_Subject
     * @return  void
     */
    public function __construct(SplSubject $caller)
    {
        // Update the caller
        $this->update($caller);
    }

    /**
     * Updates the observer subject with a new caller.
     *
     * @chainable
     * @param   object  Event_Subject
     * @return  object
     */
    public function update(SplSubject $caller)
    {
        if ( ! ($caller instanceof Event_Subject))
            throw new Kohana_Exception('event.invalid_subject', get_class($caller), get_class($this));

        // Update the caller
        $this->caller = $caller;

        return $this;
    }

    /**
     * Detaches this observer from the subject.
     *
     * @chainable
     * @return  object
     */
    public function remove()
    {
        // Detach this observer from the caller
        $this->caller->detach($this);

        return $this;
    }

    /**
     * Notify the observer of a new message. This function must be defined in
     * all observers and must take exactly one parameter of any type.
     *
     * @param   mixed   message string, object, or array
     * @return  void
     */
    abstract public function notify($message);

} // End Event Observer