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Moose::Cookbook::Roles::Recipe3(3)   User Contributed Perl Documentation  Moose::Cookbook::Roles::Recipe3(3)



NAME
       Moose::Cookbook::Roles::Recipe3 - Applying a role to an object instance

VERSION
       version 2.0205

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');

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 Moose::Meta::Role object provides an "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 "apply_all_roles" function from Moose::Util.

         apply_all_roles( $person, MyApp::Role::Job::Manager->meta );

       The main advantage of using "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 roles recipe 2.

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 nonMoose
       Moose code. For example, you could create a debugging role and apply it to an object at runtime.

AUTHOR
       Stevan Little <stevan@iinteractive.com>

COPYRIGHT AND LICENSE
       This software is copyright (c) 2011 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.



perl v5.12.5                                     2011-09-06               Moose::Cookbook::Roles::Recipe3(3)