Moose::Cookbook::Roles::Restartable_AdvancedComposition - phpMan

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
    *   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.