info > Moose::Cookbook::Roles::Restartable_AdvancedComposition

Moose::Cookbook::RMoose::Cookbook::Roles::Restartable_AdvancedComposition(3pm)

NAME
       Moose::Cookbook::Roles::Restartable_AdvancedComposition - Advanced Role
       Composition - method exclusion and aliasing

VERSION
       version 2.2200

SYNOPSIS
         package Restartable;
         use Moose::Role;

         has 'is_paused' => (
             is      => 'rw',
             isa     => 'Bool',
             default => 0,
         );

         requires 'save_state', 'load_state';

         sub stop { 1 }

         sub start { 1 }

         package Restartable::ButUnreliable;
         use Moose::Role;

         with 'Restartable' => {
             -alias => {
                 stop  => '_stop',
                 start => '_start'
             },
             -excludes => [ 'stop', 'start' ],
         };

         sub stop {
             my $self = shift;

             $self->explode() if rand(1) > .5;

             $self->_stop();
         }

         sub start {
             my $self = shift;

             $self->explode() if rand(1) > .5;

             $self->_start();
         }

         package Restartable::ButBroken;
         use Moose::Role;

         with 'Restartable' => { -excludes => [ 'stop', 'start' ] };

         sub stop {
             my $self = shift;

             $self->explode();
         }

         sub start {
             my $self = shift;

             $self->explode();
         }

DESCRIPTION
       In this example, we demonstrate how to exercise fine-grained control
       over what methods we consume from a role. We have a "Restartable" role
       which provides an "is_paused" attribute, and two methods, "stop" and
       "start".

       Then we have two more roles which implement the same interface, each
       putting their own spin on the "stop" and "start" methods.

       In the "Restartable::ButUnreliable" role, we want to provide a new
       implementation of "stop" and "start", but still have access to the
       original implementation. To do this, we alias the methods from
       "Restartable" to private methods, and provide wrappers around the
       originals (1).

       Note that aliasing simply adds a name, so we also need to exclude the
       methods with their original names.

         with 'Restartable' => {
             -alias => {
                 stop  => '_stop',
                 start => '_start'
             },
             -excludes => [ 'stop', 'start' ],
         };

       In the "Restartable::ButBroken" role, we want to provide an entirely
       new behavior for "stop" and "start". We exclude them entirely when
       composing the "Restartable" role into "Restartable::ButBroken".

       It's worth noting that the "-excludes" parameter also accepts a single
       string as an argument if you just want to exclude one method.

         with 'Restartable' => { -excludes => [ 'stop', 'start' ] };

CONCLUSION
       Exclusion and renaming are a power tool that can be handy, especially
       when building roles out of other roles. In this example, all of our
       roles implement the "Restartable" role. Each role provides same API,
       but each has a different implementation under the hood.

       You can also use the method aliasing and excluding features when
       composing a role into a class.

FOOTNOTES
       (1) The mention of wrapper should tell you that we could do the same
           thing using method modifiers, but for the sake of this example, we
           don't.

AUTHORS
       o   Stevan Little <stevan AT cpan.org>

       o   Dave Rolsky <autarch AT urth.org>

       o   Jesse Luehrs <doy AT cpan.org>

       o   Shawn M Moore <sartak AT cpan.org>

       o    ' (Yuval Kogman) <nothingmuch AT woobling.org>

       o   Karen Etheridge <ether AT cpan.org>

       o   Florian Ragwitz <rafl AT debian.org>

       o   Hans Dieter Pearcey <hdp AT cpan.org>

       o   Chris Prather <chris AT prather.org>

       o   Matt S Trout <mstrout AT cpan.org>

COPYRIGHT AND LICENSE
       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.

perl v5.34.0      Moose::Cookbook::Roles::Restartable_AdvancedComposition(3pm)