Super-Noob question

[eluser]taewoo[/eluser]
Sorry if this place is the wrong place to post but i'm a CI developer and i didn't know where to ask this... so apologies in advance.

Ok, so I never formally learned PHP... i just picked it up as I learned CI.

If i have a class and it has member "var_x"... I reference it by

Code:

$object->var_x;

But is there a way I can do this?

Code:

$field="var_x";
$object->{$field};

I remember seeing something like this in FreakAuth and i was blow away (i don't know why) but i can't seem to recall the correct method..