protected function writeCache($class, $content)
    {
        $date = date("Y-m-d h:i:s");
        $content = <<<EOD
<?php


/**
 * Generated with RoutingCacheManager
 *
 * on {$date}
 */

\$app = Slim\Slim::getInstance();

{$content}

EOD;
        $fileName = $this->cacheFile($class);
        file_put_contents($fileName, $content);

        return $fileName;
    }