Moose::Cookbook::Roles::ApplicationToInstance - Applying a role to an object instance |
Moose::Cookbook::Roles::ApplicationToInstance - Applying a role to an object instance
version 2.1605
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 ] ); $lisa->assign_work('mow the lawn');
In this recipe, we show how a role can be applied to an object. In this specific case, we are giving an employee managerial responsibilities.
Applying a role to an object is simple. The the Moose::Meta::Role manpage
object provides an apply
method. This method will do the right
thing when given an object instance.
MyApp::Role::Job::Manager->meta->apply($lisa);
We could also use the apply_all_roles
function from the Moose::Util manpage.
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 the Moose::Cookbook::Roles::Restartable_AdvancedComposition manpage.
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.
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.
Moose::Cookbook::Roles::ApplicationToInstance - Applying a role to an object instance |