6 Moose::Cookbook::Extending::Recipe2 - Providing a role for the base object class
10 package MooseX::Debugging;
14 use Moose::Util::MetaRole;
16 Moose::Exporter->setup_import_methods;
22 my $meta = Moose->init_meta(%options);
24 Moose::Util::MetaRole::apply_base_class_roles(
25 for_class => $options{for_class},
26 roles => ['MooseX::Debugging::Role::Object'],
32 package MooseX::Debugging::Role::Object;
36 after 'BUILD' => sub {
39 warn "Made a new " . ref $self . " object\n";
44 In this example, we provide a role for the base object class that adds
45 some simple debugging output. Every time an object is created, it
46 spits out a warning saying what type of object it was.
48 Obviously, a real debugging role would do something more interesting,
49 but this recipe is all about how we apply that role.
51 In this case, with the combination of L<Moose::Exporter> and
52 L<Moose::Util::MetaRole>, we ensure that when a module does C<S<use
53 MooseX::Debugging>>, it automatically gets the debugging role applied
54 to its base object class.
56 There are a few pieces of code worth looking at more closely.
58 Moose::Exporter->setup_import_methods;
60 This creates an C<import> method in the C<MooseX::Debugging>
61 package. Since we are not actually exporting anything, we do not pass
62 C<setup_import_methods> any parameters. However, we need to have an
63 C<import> method to ensure that our C<init_meta> method is called.
65 Then in our C<init_meta> method we have this line:
67 Moose->init_meta(%options);
69 This is a bit of boilerplate that almost every extension will
70 use. This ensures that the caller has a normal Moose metaclass
71 I<before> we go and add traits to it.
73 The C<< Moose->init_meta >> method does ensures that the caller has a
74 sane metaclass, and we don't want to replicate that logic in our
75 extension. If the C<< Moose->init_meta >> was already called (because
76 the caller did C<S<use Moose>> before using our extension), then
77 calling C<< Moose->init_meta >> again is effectively a no-op.
81 Dave Rolsky E<lt>autarch@urth.orgE<gt>
83 =head1 COPYRIGHT AND LICENSE
85 Copyright 2009 by Infinity Interactive, Inc.
87 L<http://www.iinteractive.com>
89 This library is free software; you can redistribute it and/or modify
90 it under the same terms as Perl itself.