Moose::Cookbook::RolMoose::Cookbook::Roles::Restartable_AdvancedComposition(3)NAMEMoose::Cookbook::Roles::Restartable_AdvancedComposition - Advanced Role
Composition - method exclusion and aliasing
VERSION
version 2.1005
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.
AUTHOR
Moose is maintained by the Moose Cabal, along with the help of many
contributors. See "CABAL" in Moose and "CONTRIBUTORS" in Moose for
details.
COPYRIGHT AND LICENSE
This software is copyright (c) 2013 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.
perl v5.18.1Moose::Cookbook::Roles::Restartable_AdvancedComposition(3)
