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moose::cookbook::meta::whymeta(3) [osx man page]

Moose::Cookbook::Meta::WhyMeta(3)			User Contributed Perl Documentation			 Moose::Cookbook::Meta::WhyMeta(3)

NAME

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

VERSION

       version 2.0604

SUMMARY

       You might want to read Moose::Manual::MOP if you haven't done so yet.

       If you've ever thought "Moose is great, but I wish it did X differently", then you've gone meta. The meta recipes demonstrate how to change
       and extend the way Moose works by extending and overriding how the meta classes (Moose::Meta::Class, Moose::Meta::Attribute, etc) work.

       The metaclass API 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 make changes to a class, for example by adding new methods or attributes.

       The interface presented by Moose.pm ("has", "with", "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 create your own Moose variant.

   Examples
       Let's say that you want to add additional properties to attributes. Specifically, we want to add a "label" property to each attribute, so
       we can write "My::Class->meta()->get_attribute('size')->label()". The first recipe shows how to do this using 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 "My::Class->meta()->table_name()".

SEE ALSO

       Many of the MooseX modules on CPAN implement metaclass extensions. A couple good examples include MooseX::Aliases and
       MooseX::UndefTolerant. For a more complex example see Fey::ORM or Bread::Board::Declare.

AUTHOR

       Moose is maintained by the Moose Cabal, along with the help of many contributors. See "CABAL" in Moose and "CONTRIBUTORS" in Moose for
       details.

COPYRIGHT AND LICENSE

       This software is copyright (c) 2012 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.

perl v5.16.2							    2012-09-19					 Moose::Cookbook::Meta::WhyMeta(3)

Check Out this Related Man Page

Moose::Cookbook::Meta::Recipe5(3)			User Contributed Perl Documentation			 Moose::Cookbook::Meta::Recipe5(3)

NAME

       Moose::Cookbook::Meta::Recipe5 - The "table" attribute as a metaclass trait

VERSION

       version 2.0205

SYNOPSIS

	 package MyApp::Meta::Class::Trait::HasTable;
	 use Moose::Role;

	 has table => (
	     is  => 'rw',
	     isa => 'Str',
	 );

	 package Moose::Meta::Class::Custom::Trait::HasTable;
	 sub register_implementation { 'MyApp::Meta::Class::Trait::HasTable' }

	 package MyApp::User;
	 use Moose -traits => 'HasTable';

	 __PACKAGE__->meta->table('User');

DESCRIPTION

       This recipe takes the metaclass table attribute from Moose::Cookbook::Meta::Recipe4 and implements it as a metaclass trait. Traits are just
       roles, as we saw in Moose::Cookbook::Meta::Recipe3.

       The advantage of using traits is that it's easy to combine multiple traits, whereas combining multiple metaclass subclasses requires
       creating yet another subclass. With traits, Moose takes care of applying them to your metaclass.

   Using this Metaclass Trait in Practice
       Once this trait has been applied to a metaclass, it looks exactly like the example we saw in Moose::Cookbook::Meta::Recipe4:

	 my $table = MyApp::User->meta->table;

	 # the safe version
	 $table = MyApp::User->meta->table
	     if MyApp::User->meta->meta->can('does')
		and MyApp::User->meta->meta->does('MyApp::Meta::Class');

       The safe version is a little complicated. We have to check that the metaclass object's metaclass has a "does" method, in which case we can
       ask if the the metaclass does a given role.

       It's simpler to just write:

	 $table = MyApp::User->meta->table
	     if MyApp::User->meta->can('table');

       In theory, this is a little less correct, since the metaclass might be getting its "table" method from a different role. In practice, you
       are unlikely to encounter this sort of problem.

SEE ALSO

       Moose::Cookbook::Meta::Recipe3 - Labels implemented via attribute traits

       Moose::Cookbook::Meta::Recipe4 - Adding a "table" attribute to the metaclass

AUTHOR

       Stevan Little <stevan@iinteractive.com>

COPYRIGHT AND LICENSE

       This software is copyright (c) 2011 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.

perl v5.12.5							    2011-09-06					 Moose::Cookbook::Meta::Recipe5(3)
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