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.IX Title "Moose::Cookbook::Roles::ApplicationToInstance 3pm"
.TH Moose::Cookbook::Roles::ApplicationToInstance 3pm 2024-03-07 "perl v5.38.2" "User Contributed Perl Documentation"
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.SH NAME
Moose::Cookbook::Roles::ApplicationToInstance \- Applying a role to an object instance
.SH VERSION
.IX Header "VERSION"
version 2.2207
.SH SYNOPSIS
.IX Header "SYNOPSIS"
.Vb 1
\&  package MyApp::Role::Job::Manager;
\&
\&  use List::Util qw( first );
\&
\&  use Moose::Role;
\&
\&  has \*(Aqemployees\*(Aq => (
\&      is  => \*(Aqrw\*(Aq,
\&      isa => \*(AqArrayRef[Employee]\*(Aq,
\&  );
\&
\&  sub assign_work {
\&      my $self = shift;
\&      my $work = shift;
\&
\&      my $employee = first { !$_\->has_work } @{ $self\->employees };
\&
\&      die \*(AqAll my employees have work to do!\*(Aq unless $employee;
\&
\&      $employee\->work($work);
\&  }
\&
\&  package main;
\&
\&  my $lisa = Employee\->new( name => \*(AqLisa\*(Aq );
\&  MyApp::Role::Job::Manager\->meta\->apply($lisa);
\&
\&  my $homer = Employee\->new( name => \*(AqHomer\*(Aq );
\&  my $bart  = Employee\->new( name => \*(AqBart\*(Aq );
\&  my $marge = Employee\->new( name => \*(AqMarge\*(Aq );
\&
\&  $lisa\->employees( [ $homer, $bart, $marge ] );
\&  $lisa\->assign_work(\*(Aqmow the lawn\*(Aq);
.Ve
.SH DESCRIPTION
.IX Header "DESCRIPTION"
In this recipe, we show how a role can be applied to an object. In
this specific case, we are giving an employee managerial
responsibilities.
.PP
Applying a role to an object is simple. The Moose::Meta::Role
object provides an \f(CW\*(C`apply\*(C'\fR method. This method will do the right
thing when given an object instance.
.PP
.Vb 1
\&  MyApp::Role::Job::Manager\->meta\->apply($lisa);
.Ve
.PP
We could also use the \f(CW\*(C`apply_all_roles\*(C'\fR function from Moose::Util.
.PP
.Vb 1
\&  apply_all_roles( $person, MyApp::Role::Job::Manager\->meta );
.Ve
.PP
The main advantage of using \f(CW\*(C`apply_all_roles\*(C'\fR is that it can be used
to apply more than one role at a time.
.PP
We could also pass parameters to the role we're applying:
.PP
.Vb 4
\&  MyApp::Role::Job::Manager\->meta\->apply(
\&      $lisa,
\&      \-alias => { assign_work => \*(Aqget_off_your_lazy_behind\*(Aq },
\&  );
.Ve
.PP
We saw examples of how method exclusion and alias working in
Moose::Cookbook::Roles::Restartable_AdvancedComposition.
.SH CONCLUSION
.IX Header "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.
.PP
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.
.SH AUTHORS
.IX Header "AUTHORS"
.IP \(bu 4
Stevan Little <stevan@cpan.org>
.IP \(bu 4
Dave Rolsky <autarch@urth.org>
.IP \(bu 4
Jesse Luehrs <doy@cpan.org>
.IP \(bu 4
Shawn M Moore <sartak@cpan.org>
.IP \(bu 4
יובל קוג'מן (Yuval Kogman) <nothingmuch@woobling.org>
.IP \(bu 4
Karen Etheridge <ether@cpan.org>
.IP \(bu 4
Florian Ragwitz <rafl@debian.org>
.IP \(bu 4
Hans Dieter Pearcey <hdp@cpan.org>
.IP \(bu 4
Chris Prather <chris@prather.org>
.IP \(bu 4
Matt S Trout <mstrout@cpan.org>
.SH "COPYRIGHT AND LICENSE"
.IX Header "COPYRIGHT AND LICENSE"
This software is copyright (c) 2006 by Infinity Interactive, Inc.
.PP
This is free software; you can redistribute it and/or modify it under
the same terms as the Perl 5 programming language system itself.