NAME
Moose::Cookbook::Roles::Recipe3 - Applying a role to an object instance
SYNOPSIS
package
MyApp::Role::Job::Manager;
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.
This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.