public function getUsingFileTimestamps($key)
    {
        $value = $this->get($this->cacheKey($key));
        $timestamps = $this->get($this->cachetskey($key));

        if ($value !== false && $timestamps !== false) {

            foreach ($timestamps as $file => $timestamp) {

                if (filemtime($file) !== $timestamp)
                    return false;
            }

            return $value;
        }

        return false;
    }