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Moose::Cookbook - How to cook a Moose


version 2.1806


The Moose cookbook is a series of recipes showing various Moose features. Most recipes present some code demonstrating some feature, and then explain the details of the code.

You should probably read the Moose::Manual first. The manual explains Moose concepts without being too code-heavy.


Basic Moose

These recipes will give you a good overview of Moose's capabilities, starting with simple attribute declaration, and moving on to more powerful features like laziness, types, type coercion, method modifiers, and more.


A simple Moose-based class. Demonstrates basic Moose attributes and subclassing.


A slightly more complex Moose class. Demonstrates using a method modifier in a subclass.


Demonstrates several attribute features, including types, weak references, predicates ("does this object have a foo?"), defaults, laziness, and triggers.


Introduces the creation and use of custom types, a BUILD method, and the use of override in a subclass. This recipe also shows how to model a set of classes that could be used to model companies, people, employees, etc.


This recipe covers more subtype creation, including the use of type coercions.


Making a class immutable greatly increases the speed of accessors and object construction.

Moose::Cookbook::Basics::BinaryTree_BuilderAndLazyBuild - Builder methods and lazy_build

The builder feature provides an inheritable and role-composable way to provide a default attribute value.


Demonstrates using operator overloading, coercion, and subtypes to model how eye color is determined during reproduction.


This recipe demonstrates the use of BUILDARGS and BUILD to hook into object construction.


In this recipe, we make a Moose-based subclass of DateTime, a module which does not use Moose itself.


Demonstrates the use of augment method modifiers, a way of turning the usual method overriding style "inside-out".

Moose Roles

These recipes will show you how to use Moose roles.


Demonstrates roles, which are also sometimes known as traits or mix-ins. Roles provide a method of code re-use which is orthogonal to subclassing.


Sometimes you just want to include part of a role in your class. Sometimes you want the whole role but one of its methods conflicts with one in your class. With method exclusion and aliasing, you can work around these problems.


In this recipe, we apply a role to an existing object instance.

Meta Moose

These recipes show you how to write your own meta classes, which lets you extend the object system provided by Moose.


If you're wondering what all this "meta" stuff is, and why you should care about it, read this "recipe".


Extending Moose's attribute metaclass is a great way to add functionality. However, attributes can only have one metaclass. Applying roles to the attribute metaclass lets you provide composable attribute functionality.


This recipe takes the class metaclass we saw in the previous recipe and reimplements it as a metaclass trait.


This recipe shows a custom method metaclass that implements making a method private.


This recipe shows an example of how you create your own meta-instance class. The meta-instance determines the internal structure of object instances and provide access to attribute slots.

In this particular instance, we use a blessed glob reference as the instance instead of a blessed hash reference.

Hooking into immutabilization (TODO)

Moose has a feature known as "immutabilization". By calling __PACKAGE__->meta()->make_immutable() after defining your class (attributes, roles, etc), you tell Moose to optimize things like object creation, attribute access, and so on.

If you are creating your own metaclasses, you may need to hook into the immutabilization system. This cuts across a number of spots, including the metaclass class, meta method classes, and possibly the meta-instance class as well.

This recipe shows you how to write extensions which immutabilize properly.

Extending Moose

These recipes cover some more ways to extend Moose, and will be useful if you plan to write your own MooseX module.


There are quite a few ways to extend Moose. This recipe provides an overview of each method, and provides recommendations for when each is appropriate.


Many base object class extensions can be implemented as roles. This example shows how to provide a base object class debugging role that is applied to any class that uses a notional MooseX::Debugging module.


This recipe shows how to provide a replacement for You may want to do this as part of the API for a MooseX module, especially if you want to default to a new metaclass class or base object class.



Legacy Recipes

These cover topics that are no longer considered best practice. We've kept them in case in you encounter these usages in the wild.




  • Stevan Little <>

  • Dave Rolsky <>

  • Jesse Luehrs <>

  • Shawn M Moore <>

  • יובל קוג'מן (Yuval Kogman) <>

  • Karen Etheridge <>

  • Florian Ragwitz <>

  • Hans Dieter Pearcey <>

  • Chris Prather <>

  • Matt S Trout <>


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.