=pod =head1 NAME Moose::Manual - What is Moose, and how do I use it? =head1 WHAT IS MOOSE? Moose is a I 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 your class, without needing to know about blessed hashrefs, accessor methods, and so on. Moose helps you define the I 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, 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 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 Introduces Moose concepts, and contrasts them against "old school" Perl 5 OO. =item L How do you make use of Moose in your classes? Now that I'm a Moose, how do I subclass something? =item L 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 Learn how objects are built in Moose, and in particular about the C, C methods. Also covers object destruction with C. =item L 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 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's type system lets you strictly define what values an attribute can contain. =item L Moose's introspection system (primarily from C) lets you ask classes about their parents, children, methods, attributes, etc. =item L 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, 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 on the prototypes and experiments Stevan did for the Perl 6 meta-model. However, Moose is B an experiment or prototype; it is for B. =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 modern, I thought it was just I? 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 object system. Nuff Said. =back =head1 AUTHOR Dave Rolsky Eautarch@urth.orgE and Stevan Little Estevan@iinteractive.comE =head1 COPYRIGHT AND LICENSE Copyright 2008 by Infinity Interactive, Inc. L This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself. =cut