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[gitmo/Moose.git] / lib / Moose / Manual.pod

=pod

=head1 NAME

Moose::Manual - What is Moose, and how do I use it?

=head1 WHAT IS MOOSE?

Moose is a I<complete> object system for Perl 5. If you've used a
modern object-oriented language (which Perl 5 definitely isn't), you
know they provide keywords for attribute declaration, object
construction, and inheritance. These keywords are part of the
language, and you don't care how they are implemented.

Moose aims to do the same thing for Perl 5 OO. We can't actually
create new keywords, but we do offer "sugar" that looks a lot like
them. More importantly, with Moose, you I<declaratively define> your
class, without needing to know about blessed hashrefs, accessor
methods, and so on.

Moose helps you define the I<logical> structure of your classes, so
you can focus on "what" rather than "how". With Moose, a class
definition reads like a list of very concise English sentences.

Moose is built in top of C<Class::MOP>, a meta-object protocol (aka
MOP). Using the MOP, Moose provides complete introspection for all
Moose-using classes. This means you can ask classes about their
attributes, parents, children, methods, etc., all using a well-defined
API. The MOP abstracts away tedious digging about in the Perl symbol
table, looking at C<@ISA> vars, and all the other crufty Perl tricks
we know and love(?).

Moose is based in large part on the Perl 6 object system, as well as
drawing on the best ideas from CLOS, Smalltalk, and many other
languages.

=head1 WHY MOOSE?

Moose makes Perl 5 OO both simpler and more powerful. It encapsulates
all the tricks of Perl 5 power users in high-level declarative APIs
which are easy to use, and doesn't require any special knowledge of
how Perl works under the hood.

If you want to dig about in the guts, Moose lets you do that too, by
using and extending its powerful introspection API.

=head1 AN EXAMPLE

  package Person;

  use Moose;

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

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

  no Moose;
  __PACKAGE__->meta->make_immutable;

This is a I<complete and usable> class definition!

  package User;

  use DateTime;
  use Moose;

  extends 'Person';

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

  has 'last_login' => (
      is      => 'rw',
      isa     => 'DateTime',
      handles => { 'date_of_last_login' => 'date' },
  );

  sub login {
      my $self = shift;
      my $pw   = shift;

      return 0 if $pw ne $self->password;

      $self->last_login( DateTime->now() );

      return 1;
  }

  no Moose;
  __PACKAGE__->meta->make_immutable;

We'll leave the line-by-line explanation of this code to other
documentation, but you can see how Moose reduces common OO idioms to
simple declarative constructs.

=head2 TABLE OF CONTENTS

This manual consists of a number of documents.

=over 4

=item L<Moose::Manual::Concepts>

Introduces Moose concepts, and contrasts them against "old school"
Perl 5 OO.

=item L<Moose::Manual::Classes>

How do you make use of Moose in your classes? Now that I'm a Moose,
how do I subclass something?

=item L<Moose::Manual::Attributes>

Attributes are a core part of the Moose OO system. An attribute is a
piece of data that an object has. Moose has a lot of attribute-related
features!

=item L<Moose::Manual::Construction>

Learn how objects are built in Moose, and in particular about the
C<BUILD>, C<BUILDARGS> methods. Also covers object destruction
with C<DEMOLISH>.

=item L<Moose::Manual::MethodModifiers>

A method modifier lets you say "before calling method X, do this
first", or "wrap method X in this code". Method modifiers are
particularly handy in roles and with attribute accessors.

=item L<Moose::Manual::Roles>

A role is something a class does (like "Debuggable" or
"Printable"). Roles provide a way of adding behavior to classes that
is orthogonal to inheritance.

=item L<Moose::Manual::Types>

Moose's type system lets you strictly define what values an attribute
can contain.

=item L<Moose::Manual::Introspection>

Moose's introspection system (primarily from C<Class::MOP>) lets you
ask classes about their parents, children, methods, attributes, etc.

=item L<Moose::Manual::MooseX>

This document shows a few of the most useful Moose extensions on CPAN.

=back

=head1 JUSTIFICATION

If you're still still asking yourself "Why do I need this?", then this
section is for you.

=over 4

=item Another object system!?!?

Yes, I know there are many, many ways to build objects in Perl 5, many
of them based on inside-out objects and other such things. Moose is
different because it is not a new object system for Perl 5, but
instead an extension of the existing object system.

Moose is built on top of L<Class::MOP>, which is a metaclass system
for Perl 5. This means that Moose not only makes building normal
Perl 5 objects better, but it also provides the power of metaclass
programming.

=item Is this for real? Or is this just an experiment?

Moose is I<based> on the prototypes and experiments Stevan did for the
Perl 6 meta-model. However, Moose is B<NOT> an experiment or
prototype; it is for B<real>.

=item Is this ready for use in production?

Yes.

Moose has been used successfully in production environments by many
people and companies. There are Moose applications which have been in
production with little or no issue now for well years. We consider it
highly stable and we are commited to keeping it stable.

Of course, in the end, you need to make this call yourself. If you
have any questions or concerns, please feel free to email Stevan, the
moose@perl.org list, or just stop by irc.perl.org#moose and ask away.

=item Is Moose just Perl 6 in Perl 5?

No. While Moose is very much inspired by Perl 6, it is not itself Perl
6.  Instead, it is an OO system for Perl 5. Stevan built Moose because
he was tired of writing the same old boring Perl 5 OO code, and
drooling over Perl 6 OO. So instead of switching to Ruby, he wrote
Moose :)

=item Wait, I<post> modern, I thought it was just I<modern>?

Stevan read Larry Wall's talk from the 1999 Linux World entitled
"Perl, the first postmodern computer language" in which he talks about
how he picked the features for Perl because he thought they were cool
and he threw out the ones that he thought sucked. This got him
thinking about how we have done the same thing in Moose. For Moose, we
have "borrowed" features from Perl 6, CLOS (LISP), Smalltalk, Java,
BETA, OCaml, Ruby and more, and the bits we didn't like (cause they
sucked) we tossed aside. So for this reason (and a few others) Stevan
has re-dubbed Moose a I<postmodern> object system.

Nuff Said.

=back

=head1 AUTHOR

Dave Rolsky E<lt>autarch@urth.orgE<gt> and Stevan Little
E<lt>stevan@iinteractive.comE<gt>

=head1 COPYRIGHT AND LICENSE

Copyright 2008 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