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.\" ========================================================================
.\"
.IX Title "Moose::Cookbook::Meta::WhyMeta 3"
.TH Moose::Cookbook::Meta::WhyMeta 3 "2021-11-07" "perl v5.26.3" "User Contributed Perl Documentation"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
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.SH "NAME"
Moose::Cookbook::Meta::WhyMeta \- Welcome to the meta world (Why Go Meta?)
.SH "VERSION"
.IX Header "VERSION"
version 2.2201
.SH "SUMMARY"
.IX Header "SUMMARY"
You might want to read Moose::Manual::MOP if you haven't done so
yet.
.PP
If you've ever thought \*(L"Moose is great, but I wish it did X
differently\*(R", 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.
.PP
The metaclass \s-1API\s0 is a set of classes that describe classes, roles,
attributes, etc. The metaclass \s-1API\s0 lets you ask questions about a
class, like \*(L"what attributes does it have?\*(R", or \*(L"what roles does the
class do?\*(R"
.PP
The metaclass system also lets you make changes to a class, for
example by adding new methods or attributes.
.PP
The interface presented by Moose.pm (\f(CW\*(C`has\*(C'\fR, \f(CW\*(C`with\*(C'\fR,
\&\f(CW\*(C`extends\*(C'\fR) is just a thin layer of syntactic sugar over the
underlying metaclass system.
.PP
By extending and changing how this metaclass system works, you can
create your own Moose variant.
.SS "Examples"
.IX Subsection "Examples"
Let's say that you want to add additional properties to
attributes. Specifically, we want to add a \*(L"label\*(R" property to each
attribute, so we can write \f(CW\*(C`My::Class\->meta()\->get_attribute(\*(Aqsize\*(Aq)\->label()\*(C'\fR. The first
recipe shows how to do this using an attribute trait.
.PP
You might also want to add additional properties to your
metaclass. For example, if you were writing an \s-1ORM\s0 based on Moose, you
could associate a table name with each class via the class's metaclass
object, letting you write \f(CW\*(C`My::Class\->meta()\->table_name()\*(C'\fR.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
Many of the MooseX modules on \s-1CPAN\s0 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.
.SH "AUTHORS"
.IX Header "AUTHORS"
.IP "\(bu" 4
Stevan Little <stevan@cpan.org>
.IP "\(bu" 4
Dave Rolsky <autarch@urth.org>
.IP "\(bu" 4
Jesse Luehrs <doy@cpan.org>
.IP "\(bu" 4
Shawn M Moore <sartak@cpan.org>
.IP "\(bu" 4
יובל קוג'מן (Yuval Kogman) <nothingmuch@woobling.org>
.IP "\(bu" 4
Karen Etheridge <ether@cpan.org>
.IP "\(bu" 4
Florian Ragwitz <rafl@debian.org>
.IP "\(bu" 4
Hans Dieter Pearcey <hdp@cpan.org>
.IP "\(bu" 4
Chris Prather <chris@prather.org>
.IP "\(bu" 4
Matt S Trout <mstrout@cpan.org>
.SH "COPYRIGHT AND LICENSE"
.IX Header "COPYRIGHT AND LICENSE"
This software is copyright (c) 2006 by Infinity Interactive, Inc.
.PP
This is free software; you can redistribute it and/or modify it under
the same terms as the Perl 5 programming language system itself.