protected function saveInCache($filename, $content)
    {
        if (empty($this->cacheDir) || ! is_dir($this->cacheDir) || ! is_writable($this->cacheDir)) {
            return false;
        }

        $content["_chk"] = filemtime($filename);

        file_put_contents(
            $this->cacheDir . DIRECTORY_SEPARATOR . basename($filename) . ".cache",
            "<?php return " . var_export($content, true) . ";"
        );

        return true;
    }