moose::cookbook::meta::whymeta(3) [mojave 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 2.1202 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. AUTHORS
o Stevan Little <stevan.little@iinteractive.com> o Dave Rolsky <autarch@urth.org> o Jesse Luehrs <doy@tozt.net> o Shawn M Moore <code@sartak.org> o XXXX XXX'XX (Yuval Kogman) <nothingmuch@woobling.org> o Karen Etheridge <ether@cpan.org> o Florian Ragwitz <rafl@debian.org> o Hans Dieter Pearcey <hdp@weftsoar.net> o Chris Prather <chris@prather.org> o Matt S Trout <mst@shadowcat.co.uk> COPYRIGHT AND LICENSE
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. perl v5.18.2 2014-01-19 Moose::Cookbook::Meta::WhyMeta(3)
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Moose::Cookbook::Legacy::Table_ClassMetaclass(3) User Contributed Perl Documentation Moose::Cookbook::Legacy::Table_ClassMetaclass(3) NAME
Moose::Cookbook::Meta::Table_ClassMetaclass - Adding a "table" attribute to the metaclass VERSION
version 2.1202 SYNOPSIS
package MyApp::Meta::Class; use Moose; extends 'Moose::Meta::Class'; has table => ( is => 'rw', isa => 'Str', ); DESCRIPTION
WARNING: Subclassing metaclasses (as opposed to providing metaclass traits) is strongly discouraged. This recipe is provided solely for reference when encountering older code that does this. In this recipe, we'll create a new metaclass which has a "table" attribute. This metaclass is for classes associated with a DBMS table, as one might do for an ORM. In this example, the table name is just a string, but in a real ORM the table might be an object describing the table. THE METACLASS
This really is as simple as the recipe "SYNOPSIS" shows. The trick is getting your classes to use this metaclass, and providing some sort of sugar for declaring the table. This is covered in Moose::Cookbook::Extending::Recipe2, which shows how to make a module like "Moose.pm" itself, with sugar like "has_table()". Using this Metaclass in Practice Accessing this new "table" attribute is quite simple. Given a class named "MyApp::User", we could simply write the following: my $table = MyApp::User->meta->table; As long as "MyApp::User" has arranged to use "MyApp::Meta::Class" as its metaclass, this method call just works. If we want to be more careful, we can check the metaclass's class: $table = MyApp::User->meta->table if MyApp::User->meta->isa('MyApp::Meta::Class'); CONCLUSION
Creating custom metaclass is trivial. Using it is a little harder, and is covered in other recipes. We will also talk about applying traits to a class metaclass, which is a more flexible and cooperative implementation. SEE ALSO
Moose::Cookbook::Meta::Recipe5 - The "table" attribute implemented as a metaclass trait Moose::Cookbook::Extending::Recipe2 - Acting like Moose.pm and providing sugar Moose-style AUTHORS
o Stevan Little <stevan.little@iinteractive.com> o Dave Rolsky <autarch@urth.org> o Jesse Luehrs <doy@tozt.net> o Shawn M Moore <code@sartak.org> o XXXX XXX'XX (Yuval Kogman) <nothingmuch@woobling.org> o Karen Etheridge <ether@cpan.org> o Florian Ragwitz <rafl@debian.org> o Hans Dieter Pearcey <hdp@weftsoar.net> o Chris Prather <chris@prather.org> o Matt S Trout <mst@shadowcat.co.uk> COPYRIGHT AND LICENSE
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. perl v5.18.2 2014-01-19 Moose::Cookbook::Legacy::Table_ClassMetaclass(3)