=pod

=head1 NAME

Moose::Manual::Classes - Making your classes use Moose (and subclassing)

=head1 USING MOOSE

Using Moose is very simple, you just C<use Moose>:

  package Person;

  use Moose;

That's it, you've made a class with Moose!

There's actually a lot going on here under the hood, so let's step
through it.

When you load L<Moose>, a bunch of sugar functions are exported into
your class. These include things like C<extends>, C<has>, C<with>, and
more. These functions are what you use to define your class. For
example, you might define an attribute ...

  package Person;

  use Moose;

  has 'ssn' => ( is => 'rw' );

Attributes are described in the L<Moose::Manual::Attributes>
documentation.

Loading Moose also enables C<strict> and C<warnings> pragmas in your
class.

When you load Moose, your class will become a subclass of
L<Moose::Object>. The L<Moose::Object> class provides a default
constructor and destructor, as well as object construction helper
methods. You can read more about this in the
L<Moose::Manual::Construction> document.

As a convenience, Moose creates a new class type for your class. See
the L<Moose::Manual::Types> document to learn more about types.

It also creates a L<Moose::Meta::Class> object for your class. This
metaclass object is now available by calling a C<meta> method on your
class, for example C<< Person->meta >>.

The metaclass object provides an introspection API for your class. It
is also used by Moose itself under the hood to add attributes, define
parent classes, and so on. In fact, all of Moose's sugar does the real
work by calling methods on this metaclass object (and other meta API
objects).

=head1 SUBCLASSING

Moose provides a simple sugar function for declaring your parent
classes, C<extends>:

  package User;

  use Moose;

  extends 'Person';

  has 'username' => ( is => 'rw' );

Note that each call to C<extends> will I<reset> your parents. For
multiple inheritance you must provide all the parents at once,
C<extends 'Foo', 'Bar'>.

You can use Moose to extend a non-Moose parent. However, when you do
this, you will inherit the parent class's constructor (assuming it is
also called C<new>). In that case, you will have to take care of
initializing attributes manually, either in the parent's constructor,
or in your subclass, and you will lose a lot of Moose magic.

=head1 NO MOOSE

Moose also allows you to remove its sugar functions from your class's
namespace. We recommend that you take advantage of this feature, since
it just makes your classes "cleaner". You can do this by simply adding
C<no Moose> at the end of your module file.

  package Person;

  use Moose;

  has 'ssn' => ( is => 'rw' );

  no Moose;

This deletes Moose's sugar functions from your class's namespace, so
that C<< Person->can('has') >> will no longer return true.

A more generic way to unimport not only L<Moose>'s exports but also
those from type libraries and other modules is to use
L<namespace::clean> or L<namespace::autoclean>.

=head1 MAKING IT FASTER

Moose has a feature called "immutabilization" that you can use to
greatly speed up your classes at runtime. However, using it does incur
a cost when your class is first being loaded. When you make your class
immutable you tell Moose that you will not be changing it in the
future. You will not be adding any more attributes, methods, roles, etc.

This allows Moose to generate code specific to your class. In
particular, it creates an "inline" constructor, making object
construction much faster.

To make your class immutable you simply call C<make_immutable> on your
class's metaclass object.

  __PACKAGE__->meta->make_immutable;

=head2 Immutabilization and C<new()>

If you override C<new()> in your class, then the immutabilization code
will not be able to provide an optimized constructor for your
class. Instead, you should use a C<BUILD()> method, which will be
called from the inlined constructor.

Alternately, if you really need to provide a different C<new()>, you
can also provide your own immutabilization method. Doing so requires
extending the Moose metaclasses, and is well beyond the scope of this
manual.

=head1 AUTHOR

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

=head1 COPYRIGHT AND LICENSE

Copyright 2008-2009 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.

=cut