private static function cache()
    {
        if (is_null(self::$memcached) && class_exists('Memcached')) {
            $servers = [['host' => '127.0.0.1', 'port' => 11211, 'weight' => 100]];

            self::$memcached = new Memcached();

            foreach ($servers as $server) {
                self::$memcached->addServer(
                    $server['host'], $server['port'], $server['weight']
                );
            }

            if (self::$memcached->getVersion() === false) {
                throw new \RuntimeException("Could not establish Memcached connection.");
            }
        }

        return self::$memcached;
    }