—=pod
=head1 NAME
Moose::Cookbook::Extending::Recipe2 - Providing a role for the base object class
=head1 SYNOPSIS
package MooseX::Debugging;
use strict;
use warnings;
use Moose ();
use Moose::Exporter;
use Moose::Util::MetaRole;
Moose::Exporter->setup_import_methods;
sub init_meta {
shift;
my %options = @_;
my $meta = Moose->init_meta(%options);
Moose::Util::MetaRole::apply_base_class_roles(
for_class => $options{for_class},
roles => ['MooseX::Debugging::Role::Object'],
);
return $meta;
}
package MooseX::Debugging::Role::Object;
use Moose::Role;
after 'BUILD' => sub {
my $self = shift;
warn "Made a new " . ref $self . " object\n";
};
=head1 DESCRIPTION
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 L<Moose::Exporter> and
L<Moose::Util::MetaRole>, we ensure that when a module does C<S<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.
Moose::Exporter->setup_import_methods;
This creates an C<import> method in the C<MooseX::Debugging>
package. Since we are not actually exporting anything, we do not pass
C<setup_import_methods> any parameters. However, we need to have an
C<import> method to ensure that our C<init_meta> method is called.
Then in our C<init_meta> method we have this line:
Moose->init_meta(%options);
This is a bit of boilerplate that almost every extension will
use. This ensures that the caller has a normal Moose metaclass
I<before> we go and add traits to it.
The C<< Moose->init_meta >> method does ensures that the caller has a
sane metaclass, and we don't want to replicate that logic in our
extension. If the C<< Moose->init_meta >> was already called (because
the caller did C<S<use Moose>> before using our extension), then
calling C<< Moose->init_meta >> again is effectively a no-op.
=head1 AUTHOR
Dave Rolsky E<lt>autarch@urth.orgE<gt>
=head1 COPYRIGHT AND LICENSE
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.
=cut