Moose::Cookbook::Meta::Recipe5(3pm)

NAME

Moose::Cookbook::Meta::Recipe5 - The "table" attribute as a metaclass
trait

SYNOPSIS

package MyApp::Meta::Class::Trait::HasTable;
use Moose::Role;

has table => (
    is  => 'rw',
    isa => 'Str',
);

package Moose::Meta::Class::Custom::Trait::HasTable;
sub register_implementation { 'MyApp::Meta::Class::Trait::HasTable' }

package MyApp::User;
use Moose -traits => 'HasTable';

__PACKAGE__->meta->table('User');

DESCRIPTION

This recipe takes the metaclass table attribute from
Moose::Cookbook::Meta::Recipe4 and implements it as a metaclass trait. Traits are just roles, as we saw in Moose::Cookbook::Meta::Recipe3.

The advantage of using traits is that it's easy to combine multiple
traits, whereas combining multiple metaclass subclasses requires
creating yet another subclass. With traits, Moose takes care of
applying them to your metaclass.

Using this Metaclass Trait in Practice

Once this trait has been applied to a metaclass, it looks exactly like the example we saw in Moose::Cookbook::Meta::Recipe4:

my $table = MyApp::User->meta->table;

# the safe version
$table = MyApp::User->meta->table

if MyApp::User->meta->meta->can('does')

and MyApp::User->meta->meta->does('MyApp::Meta::Class');

The safe version is a little complicated. We have to check that the
metaclass object's metaclass has a "does" method, in which case we can ask if the the metaclass does a given role.

It's simpler to just write:

$table = MyApp::User->meta->table

if MyApp::User->meta->can('table');

In theory, this is a little less correct, since the metaclass might be getting its "table" method from a different role. In practice, you are unlikely to encounter this sort of problem.

SEE ALSO

Moose::Cookbook::Meta::Recipe3 - Labels implemented via attribute
traits

Moose::Cookbook::Meta::Recipe4 - Adding a "table" attribute to the
metaclass

AUTHOR

Dave Rolsky <autarch@urth.org>

COPYRIGHT AND LICENSE

Copyright 2006-2010 by Infinity Interactive, Inc.

<http://www.iinteractive.com>

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

perl v5.10.1 2010-07-1Moose::Cookbook::Meta::Recipe5(3pm)