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


version 2.2206


  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;


  package main;

  my $lisa = Employee->new( name => '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 Moose::Meta::Role object provides an apply method. This method will do the right thing when given an object instance.


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:

      -alias => { assign_work => 'get_off_your_lazy_behind' },

We saw examples of how method exclusion and alias working in Moose::Cookbook::Roles::Restartable_AdvancedComposition.


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.


  • Stevan Little <>

  • Dave Rolsky <>

  • Jesse Luehrs <>

  • Shawn M Moore <>

  • יובל קוג'מן (Yuval Kogman) <>

  • Karen Etheridge <>

  • Florian Ragwitz <>

  • Hans Dieter Pearcey <>

  • Chris Prather <>

  • Matt S Trout <>


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.