Stevan Little > Moose-0.11 > Moose



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Module Version: 0.11   Source   Latest Release: Moose-2.1403


Moose - A complete modern object system for Perl 5


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


Moose is a rapidly maturing module, and is already being used by a number of people. It's test suite is growing larger by the day, and the docs should soon follow.

This said, Moose is not yet finished, and should still be considered to be evolving. Much of the outer API is stable, but the internals are still subject to change (although not without serious thought given to it).

For more details, please refer to the "FUTURE PLANS" section of this document.


Moose is an extension of the Perl 5 object system.

Another object system!?!?

Yes, I know there has been an explosion recently of new ways to build object's in Perl 5, most of them based on inside-out objects, and other such things. Moose is different because it is not a new object system for Perl 5, but instead an extension of the existing object system.

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 also provides the power of metaclass programming.

Can I use this in production? Or is this just an experiment?

Moose is based on the prototypes and experiments I did for the Perl 6 meta-model, however Moose is NOT an experiment/prototype, it is for real. I will be deploying Moose into production environments later this year, and I have all intentions of using it as my de-facto class builderfrom now on.

Is Moose just Perl 6 in Perl 5?

No. While Moose is very much inspired by Perl 6, it is not. Instead, it is an OO system for Perl 5. I built Moose because I was tired or writing the same old boring Perl 5 OO code, and drooling over Perl 6 OO. So instead of switching to Ruby, I wrote Moose :)


Moose makes every attempt to provide as much convience 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.

Unless specified with extends, any class which uses Moose will inherit from Moose::Object.

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


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


This is a method which provides access to the current class's metaclass.

extends (@superclasses)

This function will set the superclass(es) for the current class.

This approach is recommended instead of use base, 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 properly inherit from Moose::Object.

with (@roles)

This will apply a given set of @roles to the local class. Role support is currently under heavy development, see Moose::Role for more details.

has ($name, %options)

This will install an attribute of a given $name into the current class. The list of %options are the same as those provided by Class::MOP::Attribute, in addition to the list below which are provided by Moose (Moose::Meta::Attribute to be more specific):

is => 'rw'|'ro'

The is option accepts either rw (for read/write) or ro (for read only). These will create either a read/write accessor or a read-only accessor respectively, using the same name as the $name of the attribute.

If you need more control over how your accessors are named, you can use the reader, writer and accessor options inherited from Class::MOP::Attribute.

isa => $type_name

The isa option uses Moose's type constraint facilities to set up runtime type checking for this attribute. Moose will perform the checks during class construction, and within any accessors. The $type_name argument must be a string. The string can be either a class name, or a type defined using Moose's type defintion features.

coerce => (1|0)

This will attempt to use coercion with the supplied type constraint to change the value passed into any accessors of constructors. You must have supplied a type constraint in order for this to work. See Moose::Cookbook::Recipe5 for an example usage.

does => $role_name

This will accept the name of a role which the value stored in this attribute is expected to have consumed.

required => (1|0)

This marks the attribute as being required. This means a value must be supplied during class construction, and the attribute can never be set to undef with an accessor.

weak_ref => (1|0)

This will tell the class to strore the value of this attribute as a weakened reference. If an attribute is a weakened reference, it can not also be coerced.

lazy => (1|0)

This will tell the class to not create this slot until absolutely nessecary. If an attribute is marked as lazy it must have a default supplied.

auto_deref => (1|0)

This tells the accessor whether to automatically de-reference the value returned. This is only legal if your isa option is either an ArrayRef or HashRef.

trigger => $code

The trigger option is a CODE reference which will be called after the value of the attribute is set. The CODE ref will be passed the instance itself, the updated value and the attribute meta-object (this is for more advanced fiddling and can typically be ignored in most cases). You can not have a trigger on a read-only attribute.

handles => [ @handles ]

There is experimental support for attribute delegation using the handles option. More docs to come later.

before $name|@names => sub { ... }
after $name|@names => sub { ... }
around $name|@names => sub { ... }

This three items are syntactic sugar for the before, after and around method modifier features that Class::MOP provides. More information on these can be found in the Class::MOP documentation for now.


The keyword super is a noop 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.

override ($name, &sub)

An override method, is a way of explictly 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 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.

augment ($name, &sub)

An augment method, is a way of explictly 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.


This is the Carp::confess function, and exported here beause I use it all the time. This feature may change in the future, so you have been warned.


This is the Scalar::Uti::blessed function, it is exported here beause I use it all the time. It is highly recommended that this is used instead of ref anywhere you need to test for an object's class name.



Moose offers a way of removing the keywords it exports though 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    


Here is just a sampling of the plans we have in store for Moose:


What does Moose stand for??

Moose doesn't stand for one thing in particular, however, if you want, here are a few of my favorites, feel free to contribute more :)

Make Other Object Systems Envious
Makes Object Orientation So Easy
Makes Object Orientation Spiffy- Er (sorry ingy)
Most Other Object Systems Emasculate
Moose Often Ovulate Sorta Early
Moose Offers Often Super Extensions
Meta Object Orientation Syntax Extensions



I blame Sam Vilain for introducing me to the insanity that is meta-models.
I blame Audrey Tang for then encouraging my meta-model habit in #perl6.
Without Yuval "nothingmuch" Kogman this module would not be possible, and it certainly wouldn't have this name ;P
The basis of the TypeContraints module was Rob Kinyon's idea originally, I just ran with it.
Thanks to mst & chansen and the whole #moose poose for all the ideas/feature-requests/encouragement


Class::MOP documentation
The #moose channel on

This paper (suggested by lbr on #moose) was what lead to the implementation of the super/overrride and inner/augment features. If you really want to understand this feature, I suggest you read this.


All complex software has bugs lurking in it, and this module is no exception. If you find a bug please either email me, or add the bug to cpan-RT.


Stevan Little <>

Christian Hansen <>

Yuval Kogman <>


Copyright 2006 by Infinity Interactive, Inc.

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

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