Mouse::Util::MetaRole(3) Apply roles to any metaclass, as well as the object base class


package MyApp::Mouse;
use Mouse ();
use Mouse::Exporter;
use Mouse::Util::MetaRole;
use MyApp::Role::Meta::Class;
use MyApp::Role::Meta::Method::Constructor;
use MyApp::Role::Object;
Mouse::Exporter->setup_import_methods( also => 'Mouse' );
sub init_meta {
my %args = @_;
for => $args{for_class},
class_metaroles => {
class => ['MyApp::Role::Meta::Class'],
constructor => ['MyApp::Role::Meta::Method::Constructor'],
for => $args{for_class},
roles => ['MyApp::Role::Object'],
return $args{for_class}->meta();


This utility module is designed to help authors of Mouse extensions write extensions that are able to cooperate with other Mouse extensions. To do this, you must write your extensions as roles, which can then be dynamically applied to the caller's metaclasses.

This module makes sure to preserve any existing superclasses and roles already set for the meta objects, which means that any number of extensions can apply roles in any order.


It is very important that you only call this module's functions when your module is imported by the caller. The process of applying roles to the metaclass reinitializes the metaclass object, which wipes out any existing attributes already defined. However, as long as you do this when your module is imported, the caller should not have any attributes defined yet.

The easiest way to ensure that this happens is to use Mouse::Exporter, which can generate the appropriate "init_meta" method for you, and make sure it is called when imported.


This module provides two functions.

apply_metaroles( ... )

This function will apply roles to one or more metaclasses for the specified class. It accepts the following parameters:
for => $name

This specifies the class or for which to alter the meta classes. This can be a package name, or an appropriate meta-object (a Mouse::Meta::Class or Mouse::Meta::Role).

class_metaroles => \%roles

This is a hash reference specifying which metaroles will be applied to the class metaclass and its contained metaclasses and helper classes.

Each key should in turn point to an array reference of role names.

It accepts the following keys:

role_metaroles => \%roles

This is a hash reference specifying which metaroles will be applied to the role metaclass and its contained metaclasses and helper classes.

It accepts the following keys:


apply_base_class_roles( for => $class, roles => \@roles )

This function will apply the specified roles to the object's base class.