All can I say is that perldoc -f tie and the other docs are quite clear. I used to be scared by tie() myself, but in the end it results not to be that difficult... quite curiously I had a tie-related problem too this week (although it turned out not to be strictly tie specific).

Whatever, to answer your second question: it all depends on the class that implements your variable!

In particular, you use yourself the verb "to pass" rather than "to assign". And indeed assigning anything, including a reference, to a tied variable is not different than passing that "anything" to a suitable method. HTH.