Moose::Cookbook::Roles::Restartable_AdvancedComposition - Advanced Role Composition - method exclusion and aliasing |
Moose::Cookbook::Roles::Restartable_AdvancedComposition - Advanced Role Composition - method exclusion and aliasing
version 2.1605
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(); }
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' ] };
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.
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.
Moose::Cookbook::Roles::Restartable_AdvancedComposition - Advanced Role Composition - method exclusion and aliasing |