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Manual Reference Pages  -  MOOSE::COOKBOOK::ROLES::APPLICATIONTOINSTANCE (3)

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NAME

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

CONTENTS

VERSION

version 2.1605

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 Moose::Cookbook::Roles::Restartable_AdvancedComposition.

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.

AUTHORS

o Stevan Little <stevan.little@iinteractive.com>
o Dave Rolsky <autarch@urth.org>
o Jesse Luehrs <doy@tozt.net>
o Shawn M Moore <code@sartak.org>
o XXXX XXXXX (Yuval Kogman) <nothingmuch@woobling.org>
o Karen Etheridge <ether@cpan.org>
o Florian Ragwitz <rafl@debian.org>
o Hans Dieter Pearcey <hdp@weftsoar.net>
o Chris Prather <chris@prather.org>
o Matt S Trout <mst@shadowcat.co.uk>

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.

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perl v5.20.3 MOOSE::COOKBOOK::ROLES::APPLICATIONTOINSTANCE (3) 2016-02-16

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