Moose::Cookbook::Meta:UseriContributed Perl DMoose::Cookbook::Meta::Recipe5(3)NAMEMoose::Cookbook::Meta::Recipe5 - The "table" attribute as a metaclass
trait
VERSION
version 2.0402
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
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) 2012 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 v5.14.2 2012-02-04 Moose::Cookbook::Meta::Recipe5(3)
