code: private function _toClosure(callable &$callback) {
          if (!($callback instanceof \Closure))
              $callback = \Closure::fromCallable($callback);
          $callback = \Closure::bind($callback, $this, self::_getNamespace().'\\RouterWrapper');
      }
docs: 将回调函数转换为闭包并绑定当前路由实例
  
  @param callable $callback