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Moose - A postmodern object system for Perl 5


version 2.1807


package Point;
use Moose; # automatically turns on strict and warnings
has 'x' => (is => 'rw', isa => 'Int');
has 'y' => (is => 'rw', isa => 'Int');
sub clear {
    my $self = shift;
package Point3D;
use Moose;
extends 'Point';
has 'z' => (is => 'rw', isa => 'Int');
after 'clear' => sub {
    my $self = shift;


Moose is an extension of the Perl 5 object system.

The main goal of Moose is to make Perl 5 Object Oriented programming easier, more consistent, and less tedious. With Moose you can think more about what you want to do and less about the mechanics of OOP.

Additionally, Moose is built on top of Class::MOP, which is a metaclass system for Perl 5. This means that Moose not only makes building normal Perl 5 objects better, but it provides the power of metaclass programming as well.

New to Moose?

If you're new to Moose, the best place to start is the Moose::Manual docs, followed by the Moose::Cookbook. The intro will show you what Moose is, and how it makes Perl 5 OO better.

The cookbook recipes on Moose basics will get you up to speed with many of Moose's features quickly. Once you have an idea of what Moose can do, you can use the API documentation to get more detail on features which interest you.

Moose Extensions

The MooseX:: namespace is the official place to find Moose extensions. These extensions can be found on the CPAN. The easiest way to find them is to search for them (, or to examine Task::Moose which aims to keep an up-to-date, easily installable list of Moose extensions.


Much of the Moose documentation has been translated into other languages.


Moose makes every attempt to provide as much convenience as possible during class construction/definition, but still stay out of your way if you want it to. Here are a few items to note when building classes with Moose.

When you use Moose, Moose will set the class's parent class to Moose::Object, unless the class using Moose already has a parent class. In addition, specifying a parent with extends will change the parent class.

Moose will also manage all attributes (including inherited ones) that are defined with has. And (assuming you call new, which is inherited from Moose::Object) this includes properly initializing all instance slots, setting defaults where appropriate, and performing any type constraint checking or coercion.


Moose provides a number of methods to all your classes, mostly through the inheritance of Moose::Object. There is however, one exception. By default, Moose will install a method named meta in any class which uses Moose. This method returns the current class's metaclass.

If you'd like to rename this method, you can do so by passing the -meta_name option when using Moose:

use Moose -meta_name => 'my_meta';

However, the Moose::Object class also provides a method named meta which does the same thing. If your class inherits from Moose::Object (which is the default), then you will still have a meta method. However, if your class inherits from a parent which provides a meta method of its own, your class will inherit that instead.

If you'd like for Moose to not install a meta method at all, you can pass undef as the -meta_name option:

use Moose -meta_name => undef;

Again, you will still inherit meta from Moose::Object in this case.


Moose will export a number of functions into the class's namespace which may then be used to set up the class. These functions all work directly on the current class.

extends (@superclasses)

This function will set the superclass(es) for the current class. If the parent classes are not yet loaded, then extends tries to load them.

This approach is recommended instead of use base/use parent, because use base actually pushes onto the class's @ISA, whereas extends will replace it. This is important to ensure that classes which do not have superclasses still properly inherit from Moose::Object.

Each superclass can be followed by a hash reference with options. Currently, only -version is recognized:

extends 'My::Parent'      => { -version => 0.01 },
        'My::OtherParent' => { -version => 0.03 };

An exception will be thrown if the version requirements are not satisfied.

with (@roles)

This will apply a given set of @roles to the local class.

Like with extends, each specified role can be followed by a hash reference with a -version option:

with 'My::Role'      => { -version => 0.32 },
     'My::Otherrole' => { -version => 0.23 };

The specified version requirements must be satisfied, otherwise an exception will be thrown.

If your role takes options or arguments, they can be passed along in the hash reference as well.

You should only use one with, even if you are consuming multiple roles. If you consume roles using multiple with statements Moose cannot detect method conflicts between those roles.

has $name|@$names => %options

This will install an attribute of a given $name into the current class. If the first parameter is an array reference, it will create an attribute for every $name in the list. The %options will be passed to the constructor for Moose::Meta::Attribute (which inherits from Class::MOP::Attribute), so the full documentation for the valid options can be found there. These are the most commonly used options:

has +$name => %options

This is variation on the normal attribute creator has which allows you to clone and extend an attribute from a superclass or from a role. Here is an example of the superclass usage:

package Foo;
use Moose;
has 'message' => (
    is      => 'rw',
    isa     => 'Str',
    default => 'Hello, I am a Foo'
package My::Foo;
use Moose;
extends 'Foo';
has '+message' => (default => 'Hello I am My::Foo');

What is happening here is that My::Foo is cloning the message attribute from its parent class Foo, retaining the is => 'rw' and isa => 'Str' characteristics, but changing the value in default.

Here is another example, but within the context of a role:

package Foo::Role;
use Moose::Role;
has 'message' => (
    is      => 'rw',
    isa     => 'Str',
    default => 'Hello, I am a Foo'
package My::Foo;
use Moose;
with 'Foo::Role';
has '+message' => (default => 'Hello I am My::Foo');

In this case, we are basically taking the attribute which the role supplied and altering it within the bounds of this feature.

Note that you can only extend an attribute from either a superclass or a role, you cannot extend an attribute in a role that composes over an attribute from another role.

Aside from where the attributes come from (one from superclass, the other from a role), this feature works exactly the same. This feature is restricted somewhat, so as to try and force at least some sanity into it. Most options work the same, but there are some exceptions:

before $name|@names|\@names|qr/.../ => sub { ... }

after $name|@names|\@names|qr/.../ => sub { ... }

around $name|@names|\@names|qr/.../ => sub { ... }

These three items are syntactic sugar for the before, after, and around method modifier features that Class::MOP provides. More information on these may be found in Moose::Manual::MethodModifiers and the Class::MOP::Class documentation.

override ($name, &sub)

An override method is a way of explicitly saying "I am overriding this method from my superclass". You can call super within this method, and it will work as expected. The same thing can be accomplished with a normal method call and the SUPER:: pseudo-package; it is really your choice.


The keyword super is a no-op when called outside of an override method. In the context of an override method, it will call the next most appropriate superclass method with the same arguments as the original method.

augment ($name, &sub)

An augment method, is a way of explicitly saying "I am augmenting this method from my superclass". Once again, the details of how inner and augment work is best described in the Moose::Cookbook::Basics::Document_AugmentAndInner.


The keyword inner, much like super, is a no-op outside of the context of an augment method. You can think of inner as being the inverse of super; the details of how inner and augment work is best described in the Moose::Cookbook::Basics::Document_AugmentAndInner.


This is the Scalar::Util::blessed function. It is highly recommended that this is used instead of ref anywhere you need to test for an object's class name.


This is the Carp::confess function, and exported here for historical reasons.


When you use Moose, you can specify traits which will be applied to your metaclass:

use Moose -traits => 'My::Trait';

This is very similar to the attribute traits feature. When you do this, your class's meta object will have the specified traits applied to it. See "Metaclass and Trait Name Resolution" for more details.

Metaclass and Trait Name Resolution

By default, when given a trait name, Moose simply tries to load a class of the same name. If such a class does not exist, it then looks for a class matching Moose::Meta::$type::Custom::Trait::$trait_name. The $type variable here will be one of Attribute or Class, depending on what the trait is being applied to.

If a class with this long name exists, Moose checks to see if it has the method register_implementation. This method is expected to return the real class name of the trait. If there is no register_implementation method, it will fall back to using Moose::Meta::$type::Custom::Trait::$trait as the trait name.

The lookup method for metaclasses is the same, except that it looks for a class matching Moose::Meta::$type::Custom::$metaclass_name.

If all this is confusing, take a look at Moose::Cookbook::Meta::Labeled_AttributeTrait, which demonstrates how to create an attribute trait.



Moose offers a way to remove the keywords it exports, through the unimport method. You simply have to say no Moose at the bottom of your code for this to work. Here is an example:

package Person;
use Moose;
has 'first_name' => (is => 'rw', isa => 'Str');
has 'last_name'  => (is => 'rw', isa => 'Str');
sub full_name {
    my $self = shift;
    $self->first_name . ' ' . $self->last_name
no Moose; # keywords are removed from the Person package


To learn more about extending Moose, we recommend checking out the "Extending" recipes in the Moose::Cookbook, starting with Moose::Cookbook::Extending::ExtensionOverview, which provides an overview of all the different ways you might extend Moose. Moose::Exporter and Moose::Util::MetaRole are the modules which provide the majority of the extension functionality, so reading their documentation should also be helpful.

The MooseX:: namespace

Generally if you're writing an extension for Moose itself you'll want to put your extension in the MooseX:: namespace. This namespace is specifically for extensions that make Moose better or different in some fundamental way. It is traditionally not for a package that just happens to use Moose. This namespace follows from the examples of the LWPx:: and DBIx:: namespaces that perform the same function for LWP and DBI respectively.


Metaclass compatibility is a thorny subject. You should start by reading the "About Metaclass compatibility" section in the Class::MOP docs.

Moose will attempt to resolve a few cases of metaclass incompatibility when you set the superclasses for a class, in addition to the cases that Class::MOP handles.

Moose tries to determine if the metaclasses only "differ by roles". This means that the parent and child's metaclass share a common ancestor in their respective hierarchies, and that the subclasses under the common ancestor are only different because of role applications. This case is actually fairly common when you mix and match various MooseX::* modules, many of which apply roles to the metaclass.

If the parent and child do differ by roles, Moose replaces the metaclass in the child with a newly created metaclass. This metaclass is a subclass of the parent's metaclass which does all of the roles that the child's metaclass did before being replaced. Effectively, this means the new metaclass does all of the roles done by both the parent's and child's original metaclasses.

Ultimately, this is all transparent to you except in the case of an unresolvable conflict.


It should be noted that super and inner cannot be used in the same method. However, they may be combined within the same class hierarchy; see t/basics/override_augment_inner_super.t for an example.

The reason for this is that super is only valid within a method with the override modifier, and inner will never be valid within an override method. In fact, augment will skip over any override methods when searching for its appropriate inner.

This might seem like a restriction, but I am of the opinion that keeping these two features separate (yet interoperable) actually makes them easy to use, since their behavior is then easier to predict. Time will tell whether I am right or not (UPDATE: so far so good).


We offer both a mailing list and a very active IRC channel.

The mailing list is You must be subscribed to send a message. To subscribe, send an empty message to

You can also visit us at #moose on irc:// This channel is quite active, and questions at all levels (on Moose-related topics ;) are welcome.


Moose doesn't stand for one thing in particular, however, if you want, here are a few of our favorites. Feel free to contribute more!






All complex software has bugs lurking in it, and this module is no exception.

Please report any bugs to, or through the web interface at You can also submit a TODO test as a pull request at

You can also discuss feature requests or possible bugs on the Moose mailing list ( or on IRC at irc://


We are very strict about what features we add to the Moose core, especially the user-visible features. Instead we have made sure that the underlying meta-system of Moose is as extensible as possible so that you can add your own features easily.

That said, occasionally there is a feature needed in the meta-system to support your planned extension, in which case you should either email the mailing list ( or join us on IRC at irc:// to discuss. The Moose::Manual::Contributing has more detail about how and when you can contribute.


There are only a few people with the rights to release a new version of Moose. The Moose Cabal are the people to go to with questions regarding the wider purview of Moose. They help maintain not just the code but the community as well. See the list below under AUTHORS.


Moose is a community project, and as such, involves the work of many, many members of the community beyond just the members in the cabal. In particular:

Dave (autarch) Rolsky wrote most of the documentation in Moose::Manual.

John (jgoulah) Goulah wrote Moose::Cookbook::Snack::Keywords.

Jess (castaway) Robinson wrote Moose::Cookbook::Snack::Types.

Aran (bluefeet) Clary Deltac wrote Moose::Cookbook::Basics::Genome_OverloadingSubtypesAndCoercion.

Anders (Debolaz) Nor Berle contributed Test::Moose and Moose::Util.

Also, the code in Moose::Meta::Attribute::Native is based on code from the MooseX::AttributeHelpers distribution, which had contributions from:

Chris (perigrin) Prather

Cory (gphat) Watson

Evan Carroll

Florian (rafl) Ragwitz

Jason May

Jay Hannah

Jesse (doy) Luehrs

Paul (frodwith) Driver

Robert (rlb3) Boone

Robert Buels

Robert (phaylon) Sedlacek

Shawn (Sartak) Moore

Stevan Little

Tom (dec) Lanyon

Yuval Kogman

Finally, these people also contributed various tests, bug fixes, documentation, and features to the Moose codebase:


Adam (Alias) Kennedy

Christian (chansen) Hansen

Cory (gphat) Watson

Dylan Hardison (doc fixes)

Eric (ewilhelm) Wilhelm

Evan Carroll

Guillermo (groditi) Roditi

Jason May

Jay Hannah

Jonathan (jrockway) Rockway

Matt (mst) Trout

Nathan (kolibrie) Gray

Paul (frodwith) Driver

Piotr (dexter) Roszatycki

Robert Buels

Robert (phaylon) Sedlacek

Robert (rlb3) Boone

Sam (mugwump) Vilain

Scott (konobi) McWhirter

Shlomi (rindolf) Fish

Tom (dec) Lanyon

Wallace (wreis) Reis

... and many other #moose folks



This software is copyright (c) 2006 by Infinity Interactive, Inc.

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.