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# PODNAME: Moose::Cookbook::Roles::ApplicationToInstance # ABSTRACT: Applying a role to an object instance __END__ =pod =encoding UTF-8 =head1 NAME Moose::Cookbook::Roles::ApplicationToInstance - Applying a role to an object instance =head1 VERSION version 2.2203 =head1 SYNOPSIS package MyApp::Role::Job::Manager; use List::Util qw( first ); use Moose::Role; has 'employees' => ( is => 'rw', isa => 'ArrayRef[Employee]', ); sub assign_work { my $self = shift; my $work = shift; my $employee = first { !$_->has_work } @{ $self->employees }; die 'All my employees have work to do!' unless $employee; $employee->work($work); } package main; my $lisa = Employee->new( name => 'Lisa' ); MyApp::Role::Job::Manager->meta->apply($lisa); my $homer = Employee->new( name => 'Homer' ); my $bart = Employee->new( name => 'Bart' ); my $marge = Employee->new( name => 'Marge' ); $lisa->employees( [ $homer, $bart, $marge ] ); $lisa->assign_work('mow the lawn'); =head1 DESCRIPTION In this recipe, we show how a role can be applied to an object. In this specific case, we are giving an employee managerial responsibilities. Applying a role to an object is simple. The L<Moose::Meta::Role> object provides an C<apply> method. This method will do the right thing when given an object instance. MyApp::Role::Job::Manager->meta->apply($lisa); We could also use the C<apply_all_roles> function from L<Moose::Util>. apply_all_roles( $person, MyApp::Role::Job::Manager->meta ); The main advantage of using C<apply_all_roles> is that it can be used to apply more than one role at a time. We could also pass parameters to the role we're applying: MyApp::Role::Job::Manager->meta->apply( $lisa, -alias => { assign_work => 'get_off_your_lazy_behind' }, ); We saw examples of how method exclusion and alias working in L<Moose::Cookbook::Roles::Restartable_AdvancedComposition>. =begin testing-SETUP { # Not in the recipe, but needed for writing tests. package Employee; use Moose; has 'name' => ( is => 'ro', isa => 'Str', required => 1, ); has 'work' => ( is => 'rw', isa => 'Str', predicate => 'has_work', ); } =end testing-SETUP =head1 CONCLUSION Applying a role to an object instance is a useful tool for adding behavior to existing objects. In our example, it is effective used to model a promotion. It can also be useful as a sort of controlled monkey-patching for existing code, particularly non-Moose code. For example, you could create a debugging role and apply it to an object at runtime. =begin testing { my $lisa = Employee->new( name => 'Lisa' ); MyApp::Role::Job::Manager->meta->apply($lisa); my $homer = Employee->new( name => 'Homer' ); my $bart = Employee->new( name => 'Bart' ); my $marge = Employee->new( name => 'Marge' ); $lisa->employees( [ $homer, $bart, $marge ] ); $lisa->assign_work('mow the lawn'); ok( $lisa->does('MyApp::Role::Job::Manager'), 'lisa now does the manager role' ); is( $homer->work, 'mow the lawn', 'homer was assigned a task by lisa' ); } =end testing =head1 AUTHORS =over 4 =item * Stevan Little <stevan@cpan.org> =item * Dave Rolsky <autarch@urth.org> =item * Jesse Luehrs <doy@cpan.org> =item * Shawn M Moore <sartak@cpan.org> =item * יובל קוג'מן (Yuval Kogman) <nothingmuch@woobling.org> =item * Karen Etheridge <ether@cpan.org> =item * Florian Ragwitz <rafl@debian.org> =item * Hans Dieter Pearcey <hdp@cpan.org> =item * Chris Prather <chris@prather.org> =item * Matt S Trout <mstrout@cpan.org> =back =head1 COPYRIGHT AND LICENSE This software is copyright (c) 2006 by Infinity Interactive, Inc. This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself. =cut