Moose::Cookbook::Meta::Recipe5 - The "table" attribute as a metaclass trait
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');
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.
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.
does
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.
table
Moose::Cookbook::Meta::Recipe3 - Labels implemented via attribute traits
Moose::Cookbook::Meta::Recipe4 - Adding a "table" attribute to the metaclass
Dave Rolsky <autarch@urth.org>
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