ThinkPHP中M跟D函数的区别

function M($name = '', $class = 'Model')   {       static $_model = array();       if (!isset($_model[$name . '_' . $class]))           //  默认也就是 new Model($name)           $_model[$name . '_' . $class] = new $class($name);           //返回实例化对象       return $_model[$name . '_' . $class];   }  

function D($name = '', $app = ''){    static $_model = array();    if (empty($name))    //$name为空 作用就等同 函数M();        return new Model;    if (empty($app))    //默认模块名称 在Common/convention.php中定义 =@        $app = C('DEFAULT_APP');    //如果已经存在对象 直接返回    if (isset($_model[$app . $name]))        return $_model[$app . $name];    $OriClassName = $name;    //如果$name参数是以 @.**.模块名   这种参数传递的话    if (strpos($name, '.'))    {        $array = explode('.', $name);        //$name=模块名        $name = array_pop($array);        $className = $name . 'Model';        //导入Model模块所在的文件        import($app . '.Model.' . implode('.', $array) . '.' . $className);    }    //直接导入     else    {        $className = $name . 'Model';        import($app . '.Model.' . $className);    }    //实例化对象返回    if (class_exists($className))    {        $model = new $className();    } else    {        $model = new Model($name);    }    $_model[$app . $OriClassName] = $model;    return $model;}