Require Dist::Zilla 4.200016+

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

package Moose::Manual;

# ABSTRACT: What is Moose, and how do I use it?

__END__

=pod

=head1 WHAT IS MOOSE?

Moose is a I<complete> object system for Perl 5. Consider any modern
object-oriented language (which Perl 5 definitely isn't). It provides
keywords for attribute declaration, object construction, inheritance,
and maybe more. 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<define your class
declaratively>, without needing to know about blessed hashrefs,
accessor methods, and so on.

With Moose, you can concentrate on the I<logical> structure of your
classes, focusing on "what" rather than "how". A class definition with
Moose reads like a list of very concise English sentences.

Moose is built on 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 the 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
Perl 5 power tools in high-level declarative APIs which are easy to
use. Best of all, you don't need to be a wizard to use it.

But 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.

=head1 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::Unsweetened>

Shows two example classes, each written first with Moose and then with
"plain old Perl 5".

=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::Delegation>

Delegation is a powerful way to make use of attributes which are
themselves objects.

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

Learn how objects are built in Moose, and in particular about the
C<BUILD> and 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::MOP>

Moose's meta API system lets you ask classes about their parents,
children, methods, attributes, etc.

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

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

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

Moose has a lot of features, and there's definitely more than one way
to do it. However, we think that picking a subset of these features
and using them consistently makes everyone's life easier.

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

Frequently asked questions about Moose.

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

Interested in hacking on Moose? Read this.

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

This document details backwards-incompatibilities and other major
changes to Moose.

=back

=head1 JUSTIFICATION

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

=over 4

=item Another object system!?!?

Yes, we 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 years. We consider it
highly stable and we are committed 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 or
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

=cut