In the third edition of the Camel book, it is to be found on page 339, Using Closures for Private Objects
in chapter 12, Objects
I didn't personally look into it, but the authors of that book seems to think this method is a bit more secure than that...
Perl offers low-level building blocks that you can use to surround your class and its objects with an impenetrable privacy shield - one stronger, in fact, than that found in many popular object-oriented languages.
This is a very strong from of encapsulation; not only is it proof against external tampering, even other methods in the same class must use the proper access methods...
What they are talking about is using a closure as the object itself, and they proceed to give some examples. Like I said, I didn't investigate, so those claims will have to stand for the authors themselves... *grin*. I'd say they should know, though. :)
You have moved into a dark place.
It is pitch black. You are likely to be eaten by a grue.