1 package Moose::Util::MetaRole;
6 use List::MoreUtils qw( all );
8 my @Classes = qw( constructor_class destructor_class error_class );
10 sub apply_metaclass_roles {
13 my $for = $options{for_class};
15 my %old_classes = map { $_ => $for->meta->$_ } @Classes;
17 my $meta = _make_new_metaclass( $for, \%options );
19 for my $c (@Classes) {
20 if ( $options{ $c . '_roles' } ) {
21 my $class = _make_new_class(
23 $options{ $c . '_roles' }
29 $meta->$c( $old_classes{$c} );
36 sub _make_new_metaclass {
41 unless grep { exists $options->{ $_ . '_roles' } }
50 = _make_new_class( ref $for->meta(), $options->{metaclass_roles} );
52 my $old_meta = $for->meta();
54 # This could get called for a Moose::Meta::Role as well as a Moose::Meta::Class
56 $_ => _make_new_class( $old_meta->$_(), $options->{ $_ . '_roles' } )
58 grep { $old_meta->can($_) }
65 return $new_metaclass->reinitialize( $for, %classes );
68 sub apply_base_class_roles {
71 my $for = $options{for_class};
73 my $meta = $for->meta();
75 my $new_base = _make_new_class(
78 [ $meta->superclasses() ],
81 $meta->superclasses($new_base)
82 if $new_base ne $meta->name();
86 my $existing_class = shift;
88 my $superclasses = shift || [$existing_class];
90 return $existing_class unless $roles;
92 my $meta = Class::MOP::Class->initialize($existing_class);
94 return $existing_class
95 if $meta->can('does_role') && all { $meta->does_role($_) } @{$roles};
97 return Moose::Meta::Class->create_anon_class(
98 superclasses => $superclasses,
110 Moose::Util::MetaRole - Apply roles to any metaclass, as well as the object base class
114 package MyApp::Moose;
121 use Moose::Util::Meta::Role;
123 use MyApp::Role::Meta::Class;
124 use MyApp::Role::Meta::Method::Constructor;
125 use MyApp::Role::Object;
127 Moose::Exporter->setup_import_methods( also => 'Moose' );
133 Moose->init_meta(%options);
135 Moose::Util::MetaRole::apply_metaclass_roles(
136 for_class => $options{for_class},
137 metaclass_roles => ['MyApp::Role::Meta::Class'],
138 constructor_class_roles => ['MyApp::Role::Meta::Method::Constructor'],
141 Moose::Util::MetaRole::apply_base_class_roles(
142 for_class => $options{for_class},
143 roles => ['MyApp::Role::Object'],
146 return $options{for_class}->meta();
151 B<The whole concept behind this module is still considered
152 experimental, and it could go away in the future!>
154 This utility module is designed to help authors of Moose extensions
155 write extensions that are able to cooperate with other Moose
156 extensions. To do this, you must write your extensions as roles, which
157 can then be dynamically applyied to the caller's metaclasses.
159 This module makes sure to preserve any existing superclasses and roles
160 already set for the meta objects, which means that any number of
161 extensions can apply roles in any order.
165 B<It is very important that you only call this module's functions when
166 your module is imported by the caller>. The process of applying roles
167 to the metaclass reinitializes the metaclass object, which wipes out
168 any existing attributes already defined. However, as long as you do
169 this when your module is imported, the caller should not have any
170 attributes defined yet.
172 The easiest way to ensure that this happens is to use
173 L<Moose::Exporter> and provide an C<init_meta> method that will be
174 called when imported.
178 This module provides two functions.
180 =head2 apply_metaclass_roles( ... )
182 This function will apply roles to one or more metaclasses for the
183 specified class. It accepts the following parameters:
187 =item * for_class => $name
189 This specifies the class for which to alter the meta classes.
191 =item * metaclass_roles => \@roles
193 =item * attribute_metaclass_roles => \@roles
195 =item * method_metaclass_roles => \@roles
197 =item * instance_metaclass_roles => \@roles
199 =item * constructor_class_roles => \@roles
201 =item * destructor_class_roles => \@roles
203 These parameter all specify one or more roles to be applied to the
204 specified metaclass. You can pass any or all of these parameters at
209 =head2 apply_base_class_roles( for_class => $class, roles => \@roles )
211 This function will apply the specified roles to the object's base class.
213 =head1 PROBLEMS WITH METACLASS ROLES AND SUBCLASS
215 Because of the way this module works, there is an ordering problem
216 which occurs in certain situations. This sequence of events causes an
223 There is a class (ClassA) which uses some extension(s) that apply
224 roles to the metaclass.
228 You have another class (ClassB) which wants to subclass ClassA and
229 apply some more extensions.
233 Normally, the call to C<extends> will happen at run time, I<after> the
234 additional extensions are applied. This causes an error when we try to
235 make the metaclass for ClassB compatible with the metaclass for
238 We hope to be able to fix this in the future.
240 For now the workaround is for ClassB to make sure it extends ClassA
241 I<before> it loads extensions:
247 BEGIN { extends 'ClassA' }
249 use MooseX::SomeExtension;
253 Dave Rolsky E<lt>autarch@urth.orgE<gt>
255 =head1 COPYRIGHT AND LICENSE
257 Copyright 2008 by Infinity Interactive, Inc.
259 L<http://www.iinteractive.com>
261 This library is free software; you can redistribute it and/or modify
262 it under the same terms as Perl itself.