I think you'll like these
http://en.wikipedia.org/wiki/Abstract_type
http://c2.com/cgi/wiki?AbstractBaseClass
http://c2.com/cgi/wiki?AbstractClass
My understanding matches Arunbears, abstract classes aren't concrete, they can be a contract (virtual/interface), or actually do stuff (traits/roles), but you can't make an instance.

In reply to Re^5: Moose role with requirement consuming another role by Anonymous Monk
in thread Moose role with requirement consuming another role by Boldra

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