He meant something like:

```php
$serializer = strtolower($this->settings['serialize']);
if (!isset($this->_serializers[$serializer])) {
    // Exception
}
if ($serializer === 'igbinary' && !Memcached::HAVE_IGBINARY) {
    // Exception
}
if ($serializer === 'json' && !Memcached::HAVE_JSON) {
    // Exception
}
$this->_Memcached->setOption(Memcached::OPT_SERIALIZER, $serializer);
```