perldoc > Moose::Cookbook::Roles::Restartable_AdvancedComposition

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

VERSION
    version 2.2207

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
    *   Stevan Little <stevan AT cpan.org>

    *   Dave Rolsky <autarch AT urth.org>

    *   Jesse Luehrs <doy AT cpan.org>

    *   Shawn M Moore <sartak AT cpan.org>

    *   יובל קוג'מן (Yuval Kogman) <nothingmuch AT woobling.org>

    *   Karen Etheridge <ether AT cpan.org>

    *   Florian Ragwitz <rafl AT debian.org>

    *   Hans Dieter Pearcey <hdp AT cpan.org>

    *   Chris Prather <chris AT prather.org>

    *   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.