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Author image Stevan Little
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Moose::Role - The Moose Role


  package Eq;
  use Moose::Role; # automatically turns on strict and warnings

  requires 'equal';

  sub no_equal {
      my ($self, $other) = @_;

  # ... then in your classes

  package Currency;
  use Moose; # automatically turns on strict and warnings

  with 'Eq';

  sub equal {
      my ($self, $other) = @_;
      $self->as_float == $other->as_float;


Role support in Moose is pretty solid at this point. However, the best documentation is still the the test suite. It is fairly safe to assume Perl 6 style behavior and then either refer to the test suite, or ask questions on #moose if something doesn't quite do what you expect.

We are planning writing some more documentation in the near future, but nothing is ready yet, sorry.


Moose::Role currently supports all of the functions that Moose exports, but differs slightly in how some items are handled (see CAVEATS below for details).

Moose::Role also offers two role-specific keyword exports:

requires (@method_names)

Roles can require that certain methods are implemented by any class which does the role.

excludes (@role_names)

Roles can exclude other roles, in effect saying "I can never be combined with these @role_names". This is a feature which should not be used lightly.


Role support has only a few caveats:

  • Roles cannot use the extends keyword; it will throw an exception for now. The same is true of the augment and inner keywords (not sure those really make sense for roles). All other Moose keywords will be deferred so that they can be applied to the consuming class.

  • Role composition does its best to not be order-sensitive when it comes to conflict resolution and requirements detection. However, it is order-sensitive when it comes to method modifiers. All before/around/after modifiers are included whenever a role is composed into a class, and then applied in the order in which the roles are used. This also means that there is no conflict for before/around/after modifiers.

    In most cases, this will be a non-issue; however, it is something to keep in mind when using method modifiers in a role. You should never assume any ordering.

  • The requires keyword currently only works with actual methods. A method modifier (before/around/after and override) will not count as a fufillment of the requirement, and neither will an autogenerated accessor for an attribute.

    It is likely that attribute accessors will eventually be allowed to fufill those requirements, or we will introduce a requires_attr keyword of some kind instead. This decision has not yet been finalized.


All complex software has bugs lurking in it, and this module is no exception. If you find a bug please either email me, or add the bug to cpan-RT.


Stevan Little <stevan@iinteractive.com>

Christian Hansen <chansen@cpan.org>


Copyright 2006-2008 by Infinity Interactive, Inc.


This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.