in reply to Perl OO and accessors
"Hah! You're using accessors now!" Actually, I'm not. An accessor exposes an attribute.
What do you mean by "exposing"? So, if you have an implementation that uses the radius as the internal attribute and add a "set_radius" method that just does something like $self->{radius} = shift, you are using an Evil Accessor, but if you have the area as the internal attribute and add a set_radius that does $self->{area} = $PI * shift**2, you have an smart and innocent method? The interface is identical and the user shouldn't know the difference, therefore there's no way of telling, from the outside, whether a method is an accessor or not. Which leads me to the conclusion that all the ranting I hear about accessor methods is nonsense.
Now, what is a true problem is when accessor methods let the user put the object in an inconsistent state. But I call that a plain bug, not accessor evil. For example, let's say that the object stores both the radius and the area (to save recomputing the area, which as we know, is extremely expensive ;-). Then it would be bad to have a set_radius method that only does $self->{radius} = shift, because the area would be left with the wrong value. The set_radius method should be ammended to recompute the area as well.