MooseX::ClassAttribute - Declare class attributes Moose-style


version 0.29


    package My::Class;

    use Moose;
    use MooseX::ClassAttribute;

    class_has 'Cache' =>
        ( is      => 'rw',
          isa     => 'HashRef',
          default => sub { {} },


    no Moose;
    no MooseX::ClassAttribute;

    # then later ...

    My::Class->Cache()->{thing} = ...;


This module allows you to declare class attributes in exactly the same way as object attributes, using class_has() instead of has().

You can use any feature of Moose's attribute declarations, including overriding a parent's attributes, delegation (handles), attribute traits, etc. All features should just work. The one exception is the "required" flag, which is not allowed for class attributes.

The accessor methods for class attribute may be called on the class directly, or on objects of that class. Passing a class attribute to the constructor will not set that attribute.


This class exports one function when you use it, class_has(). This works exactly like Moose's has(), but it declares class attributes.

One little nit is that if you include no Moose in your class, you won't remove the class_has() function. To do that you must include no MooseX::ClassAttribute as well. Or you can just use namespace::autoclean instead.

Implementation and Immutability

This module will add a role to your class's metaclass, See MooseX::ClassAttribute::Trait::Class for details. This role provides introspection methods for class attributes.

Class attributes themselves do the MooseX::ClassAttribute::Trait::Attribute role.

Cooperation with Metaclasses and Traits

This module should work with most attribute metaclasses and traits, but it's possible that conflicts could occur. This module has been tested to work with Moose's native traits.

Class Attributes in Roles

You can add a class attribute to a role. When that role is applied to a class, the class will have the relevant class attributes added. Note that attribute defaults will be calculated when the class attribute is composed into the class.


Bugs may be submitted through the RT bug tracker (or

I am also usually active on IRC as 'drolsky' on irc://


If you'd like to thank me for the work I've done on this module, please consider making a "donation" to me via PayPal. I spend a lot of free time creating free software, and would appreciate any support you'd care to offer.

Please note that I am not suggesting that you must do this in order for me to continue working on this particular software. I will continue to do so, inasmuch as I have in the past, for as long as it interests me.

Similarly, a donation made in this way will probably not make me work on this software much more, unless I get so many donations that I can consider working on free software full time (let's all have a chuckle at that together).

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Dave Rolsky <>


  • Andrew Rodland <>

  • Karen Etheridge <>

  • Rafael Kitover <>

  • Robert Buels <>

  • Shawn M Moore <>


This software is Copyright (c) 2016 by Dave Rolsky.

This is free software, licensed under:

  The Artistic License 2.0 (GPL Compatible)