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|
=pod
=head1 NAME
Moose::Cookbook::Recipe11 - Advanced Role Composition - method exclusion and aliasing
=head1 SYNOPSIS
package Restartable;
use Moose::Role;
has 'is_paused' => (
is => 'rw',
isa => 'Bool',
default => 0,
);
requires 'save_state', 'load_state';
sub stop { ... }
sub start { ... }
package Restartable::ButUnreliable;
use Moose::Role;
with 'Restartable' => { alias => { stop => '_stop',
start => '_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();
}
=head1 DESCRIPTION
Sometimes when you include a role in a class, you may want to leave
out some of its methods. In this example, we have a role C<Restartable>
which provides an C<is_paused> attribute, and two methods, C<stop> and
C<start>. The implementation of those two methods is irrelevant.
Then we have two more roles which also implement the same interface,
each putting their own spin on the C<stop> and C<start> method.
In the C<Restartable::ButUnreliable> role, we want to provide a new
implementation of C<stop> and C<start>, but still have access to the
original implementation. To do this, we alias the methods from
C<Restartable> to private methods, and provide wrappers around the
originals (1).
In the C<Restartable::ButBroken> role, we want to provide an entirely
new behavior for C<stop> and C<start>, so we exclude them when
composing the C<Restartable> role into C<Restartable::ButBroken>.
It's worth noting that the C<excludes> parameter also accepts a single
string as an argument if you just want to exclude one method.
=head1 CONCLUSION
Method exclusion and renaming can come in handy, especially when
building roles out of other roles. In this example, all of our roles
implement the C<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.
=head1 FOOTNOTES
=over 4
=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.
=back
=head1 AUTHOR
Dave Rolsky E<lt>autarch@urth.orgE<gt>
=head1 COPYRIGHT AND LICENSE
Copyright 2006-2008 by Infinity Interactive, Inc.
L<http://www.iinteractive.com>
This library is free software; you can redistribute it and/or modify
it under the same terms as Perl itself.
=cut
|
