# PODNAME: Moose::Manual::Classes
# ABSTRACT: Making your classes use Moose (and subclassing)

=pod

=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, such as 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 the 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'>.

When you call C<extends> Moose will try to load any classes you pass.

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.

See the L<MooseX::NonMoose> module on CPAN if you're interested in extending
non-Moose parent classes with Moose child classes.

=head1 CLEANING UP MOOSE DROPPINGS

Moose exports a number of functions into your class. It's a good idea to
remove these sugar functions from your class's namespace, so that C<<
Person->can('has') >> will no longer return true.

There are several ways to do this. We recommend using L<namespace::autoclean>,
a CPAN module. Not only will it remove Moose exports, it will also remove
any other exports.

  package Person;

  use namespace::autoclean;

  use Moose;

If you absolutely can't use a CPAN module (but can use Moose?), you can write
C<no Moose> at the end of your class. This will remove any Moose exports in
your class.

  package Person;

  use Moose;

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

  no Moose;

=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 incurs
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 INSTANTIATING CLASSES

When you're ready to use Moose classes in an application, reference them in
your code in the regular Perl OO way by including a C<use> directive
at the top of the file where the objects should be created.

  use Person;

  my $person = Person->new(
    # attribute values at instantiation
    # go here
    ssn => '123456789',
  );

=cut
