I think I've read it in pretty every OO tutorial I've seen, including PBP and Damian's OO book.

The explanation seemed very obvious to me, since one is directly accessing the internal implementation of a blessed hash.

1. the internal implementation is not necessarily a hash, one can bless any ref
2. you can't change the internals anymore once they are exposed *

> Also, DBI does that as well (but uses tie) behind the curtain.

Uhm, I ignored this till now ... but DBI is a very byzantine module anyway.

But you convinced me to s/uncommon/oldfashioned/ , thanks :)

*) OK you can tie the hash/data structure, but this will slow down all internal access to any $self->{attribute}