Getting a loaded library instance: how?

[eluser]Unknown[/eluser]
I want to load a library specified in a config file as a string. Since the name of the class can change, I do to not want to hardcode it.

Code:

$authclass = $this->config->item('authenticator');
$this->load->library($authclass);

I could refer to this library statically:

Code:

$this->authenticator->foo();

But. how can I refer to this library dynamically? Something like:

Code:

$this->$authclass->foo();

Alternatively, is there a way so that:

Code:

$auth = $this->load->library($authclass);

then you'd think either this would work:

Code:

$this->$auth->foo();

or this

Code:

$auth->foo();

Thanks.