NAME¶
Moose::Cookbook::Roles::Restartable_AdvancedComposition - Advanced Role
Composition - method exclusion and aliasing
VERSION¶
version 2.1213
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.
- (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.little@iinteractive.com>
- •
- Dave Rolsky <autarch@urth.org>
- •
- Jesse Luehrs <doy@tozt.net>
- •
- Shawn M Moore <code@sartak.org>
- •
- XXXX XXX'XX (Yuval Kogman) <nothingmuch@woobling.org>
- •
- Karen Etheridge <ether@cpan.org>
- •
- Florian Ragwitz <rafl@debian.org>
- •
- Hans Dieter Pearcey <hdp@weftsoar.net>
- •
- Chris Prather <chris@prather.org>
- •
- Matt S Trout <mst@shadowcat.co.uk>
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.