Class::Mixin provides a way to mix methods from one class into another,
such that the target class can use both its methods as well as those of
the source class.
The primary advantage is that the behavior of a class can be modified
to effectively be another class without changing any of the calling
code -- just requires using the new class that mixes into the original.

WWW: http://search.cpan.org/dist/Class-Mixin/