Moose::Cookbook::Roles::Recipe3(3pm)

NAME

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

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

AUTHOR

Dave Rolsky <autarch@urth.org>

COPYRIGHT AND LICENSE

Copyright 2006-2010 by Infinity Interactive, Inc.

<http://www.iinteractive.com>

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

perl v5.10.1 2010-07-Moose::Cookbook::Roles::Recipe3(3pm)