I thought of that ... it was tempting, but being extra rigorous w/my stuff, I wanted the values inspected through direct inspection $p->{one} to be consistent with the ones done through the accessor $p->one.

FWIW, in my case, I don't need to check the value before the assignment, but immediately AFTER the assignment. For example -- wanted to be able to have a URL object where I break it down into proto,site[:port]/path, then, if I assign to $p->path, it would automatically be reflected in $p->url.