1 package Moose::Util::MetaRole;
7 $VERSION = eval $VERSION;
8 our $AUTHORITY = 'cpan:STEVAN';
10 use List::MoreUtils qw( all );
12 my @Classes = qw( constructor_class destructor_class error_class );
14 sub apply_metaclass_roles {
17 my $for = $options{for_class};
20 = map { $_ => $for->meta->$_ } grep { $for->meta->can($_) } @Classes;
22 my $meta = _make_new_metaclass( $for, \%options );
24 for my $c ( grep { $meta->can($_) } @Classes ) {
25 if ( $options{ $c . '_roles' } ) {
26 my $class = _make_new_class(
28 $options{ $c . '_roles' }
34 $meta->$c( $old_classes{$c} );
41 sub _make_new_metaclass {
46 unless grep { exists $options->{ $_ . '_roles' } }
51 wrapped_method_metaclass
56 = _make_new_class( ref $for->meta(), $options->{metaclass_roles} );
58 my $old_meta = $for->meta();
60 # This could get called for a Moose::Meta::Role as well as a Moose::Meta::Class
62 $_ => _make_new_class( $old_meta->$_(), $options->{ $_ . '_roles' } )
64 grep { $old_meta->can($_) }
68 wrapped_method_metaclass
72 return $new_metaclass->reinitialize( $for, %classes );
75 sub apply_base_class_roles {
78 my $for = $options{for_class};
80 my $meta = $for->meta();
82 my $new_base = _make_new_class(
85 [ $meta->superclasses() ],
88 $meta->superclasses($new_base)
89 if $new_base ne $meta->name();
93 my $existing_class = shift;
95 my $superclasses = shift || [$existing_class];
97 return $existing_class unless $roles;
99 my $meta = Class::MOP::Class->initialize($existing_class);
101 return $existing_class
102 if $meta->can('does_role') && all { $meta->does_role($_) } @{$roles};
104 return Moose::Meta::Class->create_anon_class(
105 superclasses => $superclasses,
117 Moose::Util::MetaRole - Apply roles to any metaclass, as well as the object base class
121 package MyApp::Moose;
128 use Moose::Util::Meta::Role;
130 use MyApp::Role::Meta::Class;
131 use MyApp::Role::Meta::Method::Constructor;
132 use MyApp::Role::Object;
134 Moose::Exporter->setup_import_methods( also => 'Moose' );
140 Moose->init_meta(%options);
142 Moose::Util::MetaRole::apply_metaclass_roles(
143 for_class => $options{for_class},
144 metaclass_roles => ['MyApp::Role::Meta::Class'],
145 constructor_class_roles => ['MyApp::Role::Meta::Method::Constructor'],
148 Moose::Util::MetaRole::apply_base_class_roles(
149 for_class => $options{for_class},
150 roles => ['MyApp::Role::Object'],
153 return $options{for_class}->meta();
158 B<The whole concept behind this module is still considered
159 experimental, and it could go away in the future!>
161 This utility module is designed to help authors of Moose extensions
162 write extensions that are able to cooperate with other Moose
163 extensions. To do this, you must write your extensions as roles, which
164 can then be dynamically applied to the caller's metaclasses.
166 This module makes sure to preserve any existing superclasses and roles
167 already set for the meta objects, which means that any number of
168 extensions can apply roles in any order.
172 B<It is very important that you only call this module's functions when
173 your module is imported by the caller>. The process of applying roles
174 to the metaclass reinitializes the metaclass object, which wipes out
175 any existing attributes already defined. However, as long as you do
176 this when your module is imported, the caller should not have any
177 attributes defined yet.
179 The easiest way to ensure that this happens is to use
180 L<Moose::Exporter> and provide an C<init_meta> method that will be
181 called when imported.
185 This module provides two functions.
187 =head2 apply_metaclass_roles( ... )
189 This function will apply roles to one or more metaclasses for the
190 specified class. It accepts the following parameters:
194 =item * for_class => $name
196 This specifies the class for which to alter the meta classes.
198 =item * metaclass_roles => \@roles
200 =item * attribute_metaclass_roles => \@roles
202 =item * method_metaclass_roles => \@roles
204 =item * wrapped_method_metaclass_roles => \@roles
206 =item * instance_metaclass_roles => \@roles
208 =item * constructor_class_roles => \@roles
210 =item * destructor_class_roles => \@roles
212 These parameter all specify one or more roles to be applied to the
213 specified metaclass. You can pass any or all of these parameters at
218 =head2 apply_base_class_roles( for_class => $class, roles => \@roles )
220 This function will apply the specified roles to the object's base class.
222 =head1 PROBLEMS WITH METACLASS ROLES AND SUBCLASS
224 Because of the way this module works, there is an ordering problem
225 which occurs in certain situations. This sequence of events causes an
232 There is a class (C<ClassA>) which uses some extension(s) that apply
233 roles to the metaclass.
237 You have another class (C<ClassB>) which wants to subclass C<ClassA> and
238 apply some more extensions.
242 Normally, the call to C<extends> will happen at run time, I<after> the
243 additional extensions are applied. This causes an error when we try to
244 make the metaclass for C<ClassB> compatible with the metaclass for
247 We hope to be able to fix this in the future.
249 For now the workaround is for C<ClassB> to make sure it extends C<ClassA>
250 I<before> it loads extensions:
256 BEGIN { extends 'ClassA' }
258 use MooseX::SomeExtension;
262 Dave Rolsky E<lt>autarch@urth.orgE<gt>
264 =head1 COPYRIGHT AND LICENSE
266 Copyright 2009 by Infinity Interactive, Inc.
268 L<http://www.iinteractive.com>
270 This library is free software; you can redistribute it and/or modify
271 it under the same terms as Perl itself.