public function cachePath($ext, $path = null)
    {
        if ($path === null) {
            if (isset($this->_data[$ext]['cachePath'])) {
                return $this->_data[$ext]['cachePath'];
            }
            return '';
        }
        $path = $this->_replacePathConstants($path);
        $this->_data[$ext]['cachePath'] = rtrim($path, '/') . '/';
    }