<?php

 class CI_Controller {

     private static $instance;

     public function __construct()

     {

         self::$instance =& $this;

         foreach (is_loaded() as $var => $class)

         {

             $this->$var =& load_class($class);

             $obj = $this->$var;

             printf("var: |%s|, class: |%s|, obj: |%s|\n\n", $var, $class, var_export($obj, true));

         }

     }

     public static function &get_instance()

     {

         return self::$instance;

     }

     public function get()

     {

         require 'model.php';

         $model = new CI_Model();

         $str = $model -> invoteClass();

         return $str;

     }

 }

 ?>

 <?php

 class CI_Model {

     public function __construct()

     {

     }

     /**

      * 这个地方的__get魔术方法使用非常巧妙，值得研究一下

      * 允许model层的类去访问对象$CI所指向的类中已经加载的类

      *

      * __get

      *

      * Allows models to access CI's loaded classes using the same

      * syntax as controllers.

      *

      * @param   string

      * @access private

      */

     public function __get($key)

     {

         $CI = &get_instance();

         printf("inner %s\n\n", __METHOD__);

         return $CI->$key;

     }

     public function invoteClass()

     {

         //$this->appa调用魔术方法__get，魔术方法__get调用类CI_Controller中的成员变量appa

         $obj = $this->appa;

         echo 'inner ' . __METHOD__ . "\n\n";

         printf("obj is: |%s|\n\n", var_export($obj, true));

         printf("obj->getApp: %s\n\n", $obj->getApp());

         $obj = $this->appb;

         echo 'inner ' . __METHOD__ . "\n\n";

         printf("obj is: |%s|\n\n", var_export($obj, true));

         printf("obj->getApp: %s\n\n", $obj->getApp());

     }

 }

 ?>

 <?php

 if ( ! function_exists('load_class'))

 {

     function &load_class($class)

     {

         static $_classes = array();

         // Does the class exist?  If so, we're done...

         // 如果要加载的类以前已经实例化过，则直接返回它

         if (isset($_classes[$class]))

         {

             return $_classes[$class];

         }

         if (file_exists($class.'.php'))

         {

             require($class.'.php');

         }

         // Keep track of what we just loaded

         //将所有加载过的类保存在静态数组_is_loaded中，

         is_loaded($class);

         //实例化类$name(比如CI_Input)，然后将实例化后的类保存在静态变量$_classes中，避免下次重复实例化

         $_classes[$class] = new $class();

         return $_classes[$class];

     }

 }

 // --------------------------------------------------------------------

 /**

 * Keeps track of which libraries have been loaded.  This function is

 * called by the load_class() function above

 *

 * @access   public

 * @return   array

 */

 if ( ! function_exists('is_loaded'))

 {

     function &is_loaded($class = '')

     {

         static $_is_loaded = array();

         if ($class != '')

         {

             $_is_loaded[strtolower($class)] = $class;

         }

         return $_is_loaded;

     }

 }

 function &get_instance()

 {

     return CI_Controller::get_instance();

 }

 ?>

 <?php

 class appA {

     public function __construct() {

     }

     public function getApp() {

         return 'this is appa';

     }

 }

 ?>

 <?php

 class appB {

     public function __construct() {

     }

     public function getApp() {

         return 'this is appb';

     }

 }

 ?>

 <?php

 require 'controller.php';

 require 'common.php';

 load_class('appA');

 load_class('appB');

 $controller = new CI_Controller();

 echo 'inner ' . __FILE__ . "\n\n";

 $controller->get();

 ?>