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[gitmo/Moose.git] / lib / Moose / Cookbook / Meta / Recipe1.pod

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=head1 NAME

Moose::Cookbook::Meta::Recipe1 - Welcome to the meta world (Why Go Meta?)

=head1 SUMMARY

If you've ever found yourself thinking "Moose is great, but I wish it
did X differently", then you've gone meta. The meta recipes are all
about how to change and extend the way Moose does its thing, by
changing how the various meta classes (C<Moose::Meta::Class>,
C<Moose::Meta::Attribute>, etc) work.

The metaclass system is a set of classes that describe classes, roles,
attributes, etc. The metaclass API lets you ask questions about a
class, like "what attributes does it have?", or "what roles does the
class do?"

The metaclass system also lets you actively make changes to a class,
for example by adding new methods.

The interface with which you normally use Moose (C<has>, C<with>,
C<extends>) is just a thin layer of syntactic sugar over the
underlying metaclass system.

By extending and changing how this metaclass system works, you can in
effect create a modified object implementation for your classes.

=head2 Examples

Let's say that you want to additional properties to
attributes. Specifically, we want to add a "label" property to each
attribute, so we can write C<<
My::Class->meta()->get_attribute('size')->label() >>. The first two
recipes show two different ways to do this, one with a full
meta-attribute subclass, and the other with an attribute trait.

You might also want to add additional properties to your
metaclass. For example, if you were writing an ORM based on Moose, you
could associate a table name with each class via the class's metaclass
object, letting you write C<< My::Class->meta()->table_name() >>.

=head1 SEE ALSO

Many of the MooseX modules on CPAN implement metaclass extensions. A
couple good examples include C<MooseX::Singleton> and
C<MooseX::AttributeHelpers>. For a more complex example see
C<Fey::ORM>.

=head1 AUTHOR

Dave Rolsky E<lt>autarch@urth.org<gt>

=head1 COPYRIGHT AND LICENSE

Copyright 2008 by Infinity Interactive, Inc.

L<http://www.iinteractive.com>

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

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