I was looking for this kind of behavior in a module I'm writing, and found this thread very useful. I'd like to point out that the functionality provided by MooseX::AttributeHelpers has been added to core Moose, and it's very slick. Read about it on CPAN: http://search.cpan.org/~drolsky/Moose-1.14/lib/Moose/Meta/Attribute/Native.pm