public function writeCache()
    {
        $cacheFile = $this->getCacheFile();
        if (!$cacheFile) {
            return;
        }
        
        if (is_writeable(dirname($cacheFile))) {
            file_put_contents(
                $cacheFile,
                sprintf(
                    '<?php return %s;',
                    var_export($this->mergedConfig, true)
                )
            );
        }
    }