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MooseX::RelatedClasses - Parameterized role for related class attributes


This document describes version 0.012 of MooseX::RelatedClasses - released August 13, 2017 as part of MooseX-RelatedClasses.


    # with this:
    with 'MooseX::RelatedClasses' => {
        name => 'Thinger', namespace => undef,

    # this:
    use MooseX::RelatedClasses;
    related_class name => 'Thinger', namespace => undef;

    # ...or this:
    use MooseX::RelatedClasses;
    related_class 'Thinger', namespace => undef;

    # ...we get three attributes:
    #   thinger_class
    #   thinger_class_traits
    #   original_thinger_class
    # ...and they look like this:

    has thinger_class => (
        traits     => [ Shortcuts ],                # MooseX::AttributeShortcuts
        is         => 'lazy',                       # MX::AttributeShortcuts
        isa        => LoadableClass,                # MooseX::Types::LoadableClass
        init_arg   => undef,
        constraint => sub { $_->isa('Thinger') },   # MX::AttributeShortcuts
        builder    => sub { ... compose original class and traits ... },

    has thinger_class_traits => (
        traits  => [ Shortcuts ],
        is      => 'lazy',
        isa     => ArrayRef[LoadableRole],
        builder => sub { [ ] },

    has original_thinger_class => (
        traits     => [ Shortcuts ],
        is         => 'lazy',
        isa        => LoadableClass,
        constraint => sub { $_->isa('Thinger') },
        coerce     => 1,
        init_arg   => 'thinger_class',
        builder    => sub { 'My::Framework::Thinger' },


Have you ever built out a framework, or interface API of some sort, to discover either that you were hardcoding your related class names (not very extension-friendly) or writing the same code for the same type of attributes to specify what related classes you're using?

Alternatively, have you ever been using a framework, and wanted to tweak one tiny bit of behaviour in a subclass, only to realize it was written in such a way to make that difficult-to-impossible without a significant effort?

This package aims to end that, by providing an easy, flexible way of defining "related classes", their base class, and allowing traits to be specified.


Parameterized roles accept parameters that influence their construction. This role accepts the following parameters.


The name of a class, without the prefix, to consider related. e.g. if My::Foo is our namespace and My::Foo::Bar is the related class:

    name => 'Bar' the correct specification.

This parameter is optional, so long as either the names or all_in_namespace parameters are given.

names [ ... ]

One or more names that would be legal for the name parameter.

all_in_namespace (Bool)

True if all findable packages under the namespace should be used as related classes. Defaults to false.


The namespace our related classes live in. If this is not given explicitly, the name of the consuming class will be used as the namespace. If the consuming class' metaclass is not available (e.g. the role is being constructed by something other than a consumer), then this parameter is mandatory.

This parameter will also accept an explicit 'undef'. If this is the case, then related classes must be specified by their full name and it is an error to attempt to enable the all_in_namespace option.


    with 'MooseX::RelatedClasses' => {
        namespace => undef,
        name      => 'LWP::UserAgent',

...will provide the lwp__user_agent_class, lwp__user_agent_traits and original_lwp__user_agent_class attributes.

load_all (Bool)

If set to true, all related classes are loaded as we find them. Defaults to false.

private (Bool)

If true, attributes, accessors and builders will all be named according to the same rules MooseX::AttributeShortcuts uses. (That is, in general prefixed with an "_".)


Synonym for "related_classes()".

Takes the same options that the role takes as parameters. That means that this:

    related_classes name => 'LWP::UserAgent', namespace => undef; effectively the same as:

    with 'MooseX::RelatedClasses' => {
        name      => 'LWP::UserAgent',
        namespace => undef,

Given a namespace, declares that everything under that namespace is related. That is,

    related_namespace 'Net::Amazon::EC2'; the same as:

    with 'MooseX::RelatedClasses' => {
        namespace        => 'Net::Amazon::EC2',
        name             => 'Net::Amazon::EC2',
        all_in_namespace => 1,


Use the "names" option with an array reference of classes, and attribute sets will be built for all of them.

    related_classes [ qw{ Thinger Dinger Finger } ];

    # or longhand:
    related_classes names => [ qw{ Thinger Dinger Finger } ];

Namespaces / Namespacing

Normally, related classes tend to be under the namespace of the class they are related to. For example, let's say we have a class named TimeLords. Related to this class are TimeLords::SoftwareWritten::Git, TimeLords::Gallifrey and TimeLords::Enemies::Daleks.

The TimeLords package can start off like this, to include the proper related classes:

    package TimeLords;

    use Moose;
    use timeandspace::autoclean;
    use MooseX::RelatedClasses;

    related_classes [ qw{ Gallifrey Enemies::Daleks SoftwareWritten::Git } ];

And that will generate the expected related class attributes:

    # TimeLords::Gallifrey
    # TimeLords::Enemies::Daleks
    # TimeLords::SoftwareWritten::Git

Occasionally you'll want to use something like LWP::UserAgent, which has nothing to do with your class except that you use it, and would like to be able to easily tweak it on the fly. This can be done with the undef namespace:

    related_class 'LWP::UserAgent', namespace => undef;

This will cause the following related class attributes to be generated:



The Class::MOP / Moose MOP show the beginnings of this: with attributes or methods named a certain way (e.g. *_metaclass()) the class to be used for a particular thing (e.g. attribute metaclass) is stored in a fashion such that a subclass (or trait) may overwrite and provide a different class name to be used.

So too, here, we do this, but in a more flexible way: we track the original related class, any additional traits that should be applied, and the new (anonymous, typically) class name of the related class.

Another example is the (very useful and usable) Net::Amazon::EC2. It uses Moose, is nicely broken out into discrete classes, etc, but does not lend itself to easy on-the-fly extension by developers with traits.


Note that we use MooseX::Traitor to compose anonymous classes, so the "anonymous names" will look less like:


And more like:


Anonymous classes are only ever composed if traits for a related class are supplied.


Please report any bugs or feature requests on the bugtracker website

When submitting a bug or request, please include a test-file or a patch to an existing test-file that illustrates the bug or desired feature.


Chris Weyl <>


Kulag <>


This software is Copyright (c) 2017, 2015, 2014, 2013, 2012 by Chris Weyl.

This is free software, licensed under:

  The GNU Lesser General Public License, Version 2.1, February 1999