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POHow do Roles and Traits differ in Moose?
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copied!<p>I have written a set of classes and interfaces that are implemented in <a href="http://search.cpan.org/~drolsky/Moose-0.87/lib/Moose.pm" rel="nofollow noreferrer">Moose</a> also using roles. What I am having trouble understanding is the exact differences in both usage and implementation of Moose traits vs. roles.</p> <p>The <a href="http://search.cpan.org/~drolsky/Moose-0.87/lib/Moose/Cookbook/Extending/Recipe1.pod#ROLES_VS_TRAITS_VS_SUBCLASSES" rel="nofollow noreferrer">Moose documentation</a> states:</p> <blockquote> <p>It is important to understand that roles and traits are the same thing. A role can be used as a trait, and a trait is a role. The only thing that distinguishes the two is that a trait is packaged in a way that lets Moose resolve a short name to a class name. In other words, with a trait, the caller can refer to it by a short name like "Big", and Moose will resolve it to a class like MooseX::Embiggen::Meta::Attribute::Role::Big.</p> </blockquote> <p>It is my understanding that traits and roles are "the same". However, when implementing a basic test of the idea using the <code>use Moose -traits 'Foo'</code> syntax does not seem to do what I would expect. Surely I must be missing something here. </p> <p>This first example fails with "Can't locate object method 'foo'"</p> <pre><code>package MyApp::Meta::Class::Trait::HasTable; use Moose::Role; sub foo { warn 'foo' } package Moose::Meta::Class::Custom::Trait::HasTable; sub register_implementation { 'MyApp::Meta::Class::Trait::HasTable' } package MyApp::User; use Moose -traits => 'HasTable'; __PACKAGE__->foo(); #Can't locate object method 'foo' </code></pre> <p>Compared to this one (which does work):</p> <pre><code>package MyApp::Meta::Class::Trait::HasTable; use Moose::Role; sub foo { warn 'foo' } package Moose::Meta::Class::Custom::Trait::HasTable; sub register_implementation { 'MyApp::Meta::Class::Trait::HasTable' } package MyApp::User; use Moose; with 'MyApp::Meta::Class::Trait::HasTable'; __PACKAGE__->foo(); #foo </code></pre>

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