A quick CPAN search for "interface" brings up the interface module. That looks promising. It references Class::Contract, which may be a little too much koolaid for you, but it would definitely do what you're looking for. :-)
My criteria for good software:
  1. Does it work?
  2. Can someone else come in, make a change, and be reasonably certain no bugs were introduced?

In reply to Re^3: Class capabilities by dragonchild
in thread Class capabilities by Ovid

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