Moose (Perl): access attribute definitions in base classes

Question

Using __PACKAGE__->meta->get_attribute('foo'), you can access the foo attribute definitions in a given class, which can be useful.

#!perl
package Bla;
use Moose;
has bla => is => 'ro', isa => 'Str';
has hui => is => 'ro', isa => 'Str', required => 1;
no Moose; __PACKAGE__->meta->make_immutable;

package Blub;
use Moose;
has bla => is => 'ro', isa => 'Str';
has hui => is => 'ro', isa => 'Str', required => 0;
no Moose; __PACKAGE__->meta->make_immutable;

package Blubbel;
use Moose;
extends 'Blub';
no Moose; __PACKAGE__->meta->make_immutable;

package main;
use Test::More;
use Test::Exception;

my $attr = Bla->meta->get_attribute('hui');
is $attr->is_required, 1;

$attr = Blub->meta->get_attribute('hui');
is $attr->is_required, 0;

$attr = Blubbel->meta->get_attribute('hui');
is $attr, undef;
throws_ok { $attr->is_required }
  qr/Can't call method "is_required" on an undefined value/;
diag 'Attribute aus Basisklassen werden hier nicht gefunden.';

done_testing;

As evidenced by this little code sample, however, this cannot be used to access attribute definitions in base classes, which would be even more useful for my particular case. Is there a way to achieve what I want?

score 9 · Accepted Answer · answered Jun 03 '11 at 16:10

NOTE that get_attribute does not search superclasses, for that you need to use find_attribute_by_name

— Class::MOP::Class docs. And indeed this code passes:

my $attr = Bla->meta->find_attribute_by_name('hui');
is $attr->is_required, 1;

$attr = Blub->meta->find_attribute_by_name('hui');
is $attr->is_required, 0;

$attr = Blubbel->meta->find_attribute_by_name('hui');
is $attr->is_required, 0;

Moose (Perl): access attribute definitions in base classes

1 Answers1