1. No, because that's a terrible idea. If I've created a class, why shouldn't you be able to inherit from it?
Because it may not be safe to do so, e.g. from Method Privacy in Perl
Recently I was writing a subclass of somebody else's class and noticed it suddenly started behaving strangely. After an embarrassing amount of time spent debugging I discovered that one of my underscore methods happened to have the same name as one of the superclass' underscore methods (actually two levels up inheritance), so was getting called by the superclass when I hadn't expected it to be.
Whereas a construct for disallowing inheritance (on a per class basis) would make it clear to a would be subclasser that the class wasn't designed for inheritance.

But the OP was asking about how (as an author) they can stop their classes from being subclassed. I think this is totally legitimate from a design point of view given all the design warts of inheritance:

In reply to Re^2: Perl OOP by Arunbear
in thread Perl OOP by QueenSvetlana

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