Class::Null, on its way to CPAN, implements the Null Class design pattern. The code is exceedingly simple, but the manpage explains the concept in some detail. This class is a by-product of the design for a class system for one of the projects I'm working on. The study of design patterns is actually pretty interesting. Object-Oriented Analysis and Design (OOA and OOD) should be rewarding topics to work on (both intellectually and financially). And it's a chance to show people how much more elegant that pattern could be implemented if they'd just use Perl...
