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.IX Title "Moose::Cookbook::Roles::Restartable_AdvancedComposition 3"
.TH Moose::Cookbook::Roles::Restartable_AdvancedComposition 3 "2021-11-07" "perl v5.26.3" "User Contributed Perl Documentation"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
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.if n .ad l
.nh
.SH "NAME"
Moose::Cookbook::Roles::Restartable_AdvancedComposition \- Advanced Role Composition \- method exclusion and aliasing
.SH "VERSION"
.IX Header "VERSION"
version 2.2201
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 2
\&  package Restartable;
\&  use Moose::Role;
\&
\&  has \*(Aqis_paused\*(Aq => (
\&      is      => \*(Aqrw\*(Aq,
\&      isa     => \*(AqBool\*(Aq,
\&      default => 0,
\&  );
\&
\&  requires \*(Aqsave_state\*(Aq, \*(Aqload_state\*(Aq;
\&
\&  sub stop { 1 }
\&
\&  sub start { 1 }
\&
\&  package Restartable::ButUnreliable;
\&  use Moose::Role;
\&
\&  with \*(AqRestartable\*(Aq => {
\&      \-alias => {
\&          stop  => \*(Aq_stop\*(Aq,
\&          start => \*(Aq_start\*(Aq
\&      },
\&      \-excludes => [ \*(Aqstop\*(Aq, \*(Aqstart\*(Aq ],
\&  };
\&
\&  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 \*(AqRestartable\*(Aq => { \-excludes => [ \*(Aqstop\*(Aq, \*(Aqstart\*(Aq ] };
\&
\&  sub stop {
\&      my $self = shift;
\&
\&      $self\->explode();
\&  }
\&
\&  sub start {
\&      my $self = shift;
\&
\&      $self\->explode();
\&  }
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
In this example, we demonstrate how to exercise fine-grained control
over what methods we consume from a role. We have a \f(CW\*(C`Restartable\*(C'\fR
role which provides an \f(CW\*(C`is_paused\*(C'\fR attribute, and two methods,
\&\f(CW\*(C`stop\*(C'\fR and \f(CW\*(C`start\*(C'\fR.
.PP
Then we have two more roles which implement the same interface, each
putting their own spin on the \f(CW\*(C`stop\*(C'\fR and \f(CW\*(C`start\*(C'\fR methods.
.PP
In the \f(CW\*(C`Restartable::ButUnreliable\*(C'\fR role, we want to provide a new
implementation of \f(CW\*(C`stop\*(C'\fR and \f(CW\*(C`start\*(C'\fR, but still have access to the
original implementation. To do this, we alias the methods from
\&\f(CW\*(C`Restartable\*(C'\fR to private methods, and provide wrappers around the
originals (1).
.PP
Note that aliasing simply \fIadds\fR a name, so we also need to exclude the
methods with their original names.
.PP
.Vb 7
\&  with \*(AqRestartable\*(Aq => {
\&      \-alias => {
\&          stop  => \*(Aq_stop\*(Aq,
\&          start => \*(Aq_start\*(Aq
\&      },
\&      \-excludes => [ \*(Aqstop\*(Aq, \*(Aqstart\*(Aq ],
\&  };
.Ve
.PP
In the \f(CW\*(C`Restartable::ButBroken\*(C'\fR role, we want to provide an entirely
new behavior for \f(CW\*(C`stop\*(C'\fR and \f(CW\*(C`start\*(C'\fR. We exclude them entirely when
composing the \f(CW\*(C`Restartable\*(C'\fR role into \f(CW\*(C`Restartable::ButBroken\*(C'\fR.
.PP
It's worth noting that the \f(CW\*(C`\-excludes\*(C'\fR parameter also accepts a single
string as an argument if you just want to exclude one method.
.PP
.Vb 1
\&  with \*(AqRestartable\*(Aq => { \-excludes => [ \*(Aqstop\*(Aq, \*(Aqstart\*(Aq ] };
.Ve
.SH "CONCLUSION"
.IX Header "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 \f(CW\*(C`Restartable\*(C'\fR role. Each role provides same \s-1API,\s0
but each has a different implementation under the hood.
.PP
You can also use the method aliasing and excluding features when
composing a role into a class.
.SH "FOOTNOTES"
.IX Header "FOOTNOTES"
.IP "(1)" 4
.IX Item "(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.
.SH "AUTHORS"
.IX Header "AUTHORS"
.IP "\(bu" 4
Stevan Little <stevan@cpan.org>
.IP "\(bu" 4
Dave Rolsky <autarch@urth.org>
.IP "\(bu" 4
Jesse Luehrs <doy@cpan.org>
.IP "\(bu" 4
Shawn M Moore <sartak@cpan.org>
.IP "\(bu" 4
יובל קוג'מן (Yuval Kogman) <nothingmuch@woobling.org>
.IP "\(bu" 4
Karen Etheridge <ether@cpan.org>
.IP "\(bu" 4
Florian Ragwitz <rafl@debian.org>
.IP "\(bu" 4
Hans Dieter Pearcey <hdp@cpan.org>
.IP "\(bu" 4
Chris Prather <chris@prather.org>
.IP "\(bu" 4
Matt S Trout <mstrout@cpan.org>
.SH "COPYRIGHT AND LICENSE"
.IX Header "COPYRIGHT AND LICENSE"
This software is copyright (c) 2006 by Infinity Interactive, Inc.
.PP
This is free software; you can redistribute it and/or modify it under
the same terms as the Perl 5 programming language system itself.