View on
MetaCPAN is shutting down
For details read Perl NOC. After June 25th this page will redirect to
Stevan Little > Moose-1.00 > Moose::Cookbook::Extending::Recipe2


Annotate this POD


New  10
Open  42
Stalled  11
View/Report Bugs
Source   Latest Release: Moose-2.0204


Moose::Cookbook::Extending::Recipe2 - Providing a role for the base object class


  package MooseX::Debugging;

  use Moose::Exporter;

      base_class_roles => ['MooseX::Debugging::Role::Object'],

  package MooseX::Debugging::Role::Object;

  use Moose::Role;

  after 'BUILDALL' => sub {
      my $self = shift;

      warn "Made a new " . ( ref $self ) . " object\n";


In this example, we provide a role for the base object class that adds some simple debugging output. Every time an object is created, it spits out a warning saying what type of object it was.

Obviously, a real debugging role would do something more interesting, but this recipe is all about how we apply that role.

In this case, with the combination of Moose::Exporter and Moose::Util::MetaRole, we ensure that when a module does use MooseX::Debugging, it automatically gets the debugging role applied to its base object class.

There are a few pieces of code worth looking at more closely.

      base_class_roles => ['MooseX::Debugging::Role::Object'],

This creates an import method in the MooseX::Debugging package. Since we are not actually exporting anything, we do not pass setup_import_methods any parameters related to exports, but we need to have an import method to ensure that our init_meta method is called. The init_meta is created by setup_import_methods for us, since we passed the base_class_roles parameter. The generated init_meta will in turn call Moose::Util::MetaRole::apply_base_class_roles.


Dave Rolsky <>


Copyright 2009 by Infinity Interactive, Inc.

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

syntax highlighting: