NAME¶
Moose::Manual - What is Moose, and how do I use it?
VERSION¶
version 2.0603
WHAT IS MOOSE?¶
Moose is a
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
define your class declaratively,
without needing to know about blessed hashrefs, accessor methods, and so on.
With Moose, you can concentrate on the
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 "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 @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.
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.
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
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.
TABLE OF CONTENTS¶
This manual consists of a number of documents.
- Moose::Manual::Concepts
- Introduces Moose concepts, and contrasts them against
"old school" Perl 5 OO.
- Moose::Manual::Unsweetened
- Shows two example classes, each written first with Moose
and then with "plain old Perl 5".
- Moose::Manual::Classes
- How do you make use of Moose in your classes? Now that I'm
a Moose, how do I subclass something?
- 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!
- Moose::Manual::Delegation
- Delegation is a powerful way to make use of attributes
which are themselves objects.
- Moose::Manual::Construction
- Learn how objects are built in Moose, and in particular
about the "BUILD" and "BUILDARGS" methods. Also covers
object destruction with "DEMOLISH".
- 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.
- 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.
- Moose::Manual::Types
- Moose's type system lets you strictly define what values an
attribute can contain.
- Moose::Manual::MOP
- Moose's meta API system lets you ask classes about their
parents, children, methods, attributes, etc.
- Moose::Manual::MooseX
- This document describes a few of the most useful Moose
extensions on CPAN.
- 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.
- Moose::Manual::FAQ
- Frequently asked questions about Moose.
- Moose::Manual::Contributing
- Interested in hacking on Moose? Read this.
- Moose::Manual::Delta
- This document details backwards-incompatibilities and other
major changes to Moose.
JUSTIFICATION¶
If you're still asking yourself "Why do I need this?", then this
section is for you.
- 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 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.
- Is this for real? Or is this just an experiment?
- Moose is based on the prototypes and experiments
Stevan did for the Perl 6 meta-model. However, Moose is NOT an
experiment or prototype; it is for real.
- 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.
- 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
:)
- Wait, post modern, I thought it was just
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 postmodern object system.
Nuff Said.
AUTHOR¶
Moose is maintained by the Moose Cabal, along with the help of many
contributors. See "CABAL" in Moose and "CONTRIBUTORS" in
Moose for details.
COPYRIGHT AND LICENSE¶
This software is copyright (c) 2012 by Infinity Interactive, Inc..
This is free software; you can redistribute it and/or modify it under the same
terms as the Perl 5 programming language system itself.