public function load_plugins($subtype) {
        global $CFG;
        $result = array();

        $names = core_component::get_plugin_list($subtype);

        foreach ($names as $name => $path) {
            if (file_exists($path . '/locallib.php')) {
                require_once($path . '/locallib.php');

                $shortsubtype = substr($subtype, strlen('assign'));
                $pluginclass = 'assign_' . $shortsubtype . '_' . $name;

                $plugin = new $pluginclass($this, $name);

                if ($plugin instanceof assign_plugin) {
                    $idx = $plugin->get_sort_order();
                    while (array_key_exists($idx, $result)) {
                        $idx +=1;
                    }
                    $result[$idx] = $plugin;
                }
            }
        }
        ksort($result);
        return $result;
    }