154 lines
3.4 KiB
Plaintext
154 lines
3.4 KiB
Plaintext
# PODNAME: Moose::Cookbook::Extending::Debugging_BaseClassRole
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# ABSTRACT: Providing a role for the base object class
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__END__
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=pod
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=encoding UTF-8
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=head1 NAME
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Moose::Cookbook::Extending::Debugging_BaseClassRole - Providing a role for the base object class
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=head1 VERSION
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version 2.2207
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=head1 SYNOPSIS
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package MooseX::Debugging;
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use Moose::Exporter;
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Moose::Exporter->setup_import_methods(
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base_class_roles => ['MooseX::Debugging::Role::Object'],
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);
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package MooseX::Debugging::Role::Object;
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use Moose::Role;
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sub BUILD {}
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after BUILD => sub {
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my $self = shift;
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warn "Made a new " . ( ref $self ) . " object\n";
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};
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=head1 DESCRIPTION
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In this example, we provide a role for the base object class that adds
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some simple debugging output. Every time an object is created, it
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spits out a warning saying what type of object it was.
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Obviously, a real debugging role would do something more interesting,
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but this recipe is all about how we apply that role.
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In this case, with the combination of L<Moose::Exporter> and
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L<Moose::Util::MetaRole>, we ensure that when a module does C<S<use
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MooseX::Debugging>>, it automatically gets the debugging role applied
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to its base object class.
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There are a few pieces of code worth looking at more closely.
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Moose::Exporter->setup_import_methods(
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base_class_roles => ['MooseX::Debugging::Role::Object'],
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);
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This creates an C<import> method in the C<MooseX::Debugging> package. Since we
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are not actually exporting anything, we do not pass C<setup_import_methods>
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any parameters related to exports, but we need to have an C<import> method to
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ensure that our C<init_meta> method is called. The C<init_meta> is created by
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C<setup_import_methods> for us, since we passed the C<base_class_roles>
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parameter. The generated C<init_meta> will in turn call
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L<Moose::Util::MetaRole::apply_base_class_roles|Moose::Util::MetaRole/apply_base_class_roles>.
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sub BUILD {}
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after BUILD => sub {
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...
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};
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Due to the way role composition currently works, if the class that a role is
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composed into contains a C<BUILD> method, then that will override the C<BUILD>
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method in any roles it composes, which is typically not what you want. Using a
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method modifier on C<BUILD> avoids this issue, since method modifiers compose
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together rather than being overridden. Method modifiers require that a method
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exists in order to wrap, however, so we also provide a stub method to wrap if
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no C<BUILD> method exists in the class.
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=for testing-SETUP use Test::Needs 'Test::Output';
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use Test::Output;
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=begin testing
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{
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package Debugged;
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use Moose;
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MooseX::Debugging->import;
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}
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stderr_is(
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sub { Debugged->new },
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"Made a new Debugged object\n",
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'got expected output from debugging role'
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);
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=end testing
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=head1 AUTHORS
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=over 4
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=item *
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Stevan Little <stevan@cpan.org>
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=item *
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Dave Rolsky <autarch@urth.org>
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=item *
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Jesse Luehrs <doy@cpan.org>
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=item *
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Shawn M Moore <sartak@cpan.org>
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=item *
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יובל קוג'מן (Yuval Kogman) <nothingmuch@woobling.org>
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=item *
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Karen Etheridge <ether@cpan.org>
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=item *
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Florian Ragwitz <rafl@debian.org>
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=item *
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Hans Dieter Pearcey <hdp@cpan.org>
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=item *
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Chris Prather <chris@prather.org>
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=item *
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Matt S Trout <mstrout@cpan.org>
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=back
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=head1 COPYRIGHT AND LICENSE
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This software is copyright (c) 2006 by Infinity Interactive, Inc.
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This is free software; you can redistribute it and/or modify it under
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the same terms as the Perl 5 programming language system itself.
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=cut
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