NAME

Moose - A postmodern object system for Perl 5

SYNOPSIS

package Point; use Moose; # automatically turns on strict and warnings has 'x' => (is => 'rw', isa => 'Int'); has 'y' => (is => 'rw', isa => 'Int'); sub clear { my $self = shift; $self->x(0); $self->y(0); } package Point3D; use Moose; extends 'Point'; has 'z' => (is => 'rw', isa => 'Int'); after 'clear' => sub { my $self = shift; $self->z(0); };

DESCRIPTION

Moose is an extension of the Perl 5 object system.

The main goal of Moose is to make Perl 5 Object Oriented programming easier, more consistent and less tedious. With Moose you can to think more about what you want to do and less about the mechanics of OOP.

Additionally, 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 provides the power of metaclass programming as well.

New to Moose?

If you're new to Moose, the best place to start is the Moose::Intro docs, followed by the Moose::Cookbook. The intro will show you what Moose is, and how it makes Perl 5 OO better.

The cookbook recipes on Moose basics will get you up to speed with many of Moose's features quickly. Once you have an idea of what Moose can do, you can use the API documentation to get more detail on features which interest you.

Moose Extensions

The MooseX:: namespace is the official place to find Moose extensions. These extensions can be found on the CPAN. The easiest way to find them is to search for them (http://search.cpan.org/search?query=MooseX::), or to examine Task::Moose which aims to keep an up-to-date, easily installable list of Moose extensions.

BUILDING CLASSES WITH MOOSE

Moose makes every attempt to provide as much convenience as possible during class construction/definition, but still stay out of your way if you want it to. Here are a few items to note when building classes with Moose.

Unless specified with extends , any class which uses Moose will inherit from Moose::Object.

Moose will also manage all attributes (including inherited ones) that are defined with has . And (assuming you call new , which is inherited from Moose::Object) this includes properly initializing all instance slots, setting defaults where appropriate, and performing any type constraint checking or coercion.

PROVIDED METHODS

Moose provides a number of methods to all your classes, mostly through the inheritance of Moose::Object. There is however, one exception.

This is a method which provides access to the current class's metaclass.

EXPORTED FUNCTIONS

Moose will export a number of functions into the class's namespace which may then be used to set up the class. These functions all work directly on the current class.

extends (@superclasses) This function will set the superclass(es) for the current class. This approach is recommended instead of use base , because use base actually push es onto the class's @ISA , whereas extends will replace it. This is important to ensure that classes which do not have superclasses still properly inherit from Moose::Object. with (@roles) This will apply a given set of @roles to the local class. has $name => %options This will install an attribute of a given $name into the current class. The %options are the same as those provided by Class::MOP::Attribute, in addition to the list below which are provided by Moose (Moose::Meta::Attribute to be more specific): is => 'rw'|'ro' The is option accepts either rw (for read/write) or ro (for read only). These will create either a read/write accessor or a read-only accessor respectively, using the same name as the $name of the attribute. If you need more control over how your accessors are named, you can use the reader, writer and accessor options inherited from Class::MOP::Attribute, however if you use those, you won't need the is option. isa => $type_name The isa option uses Moose's type constraint facilities to set up runtime type checking for this attribute. Moose will perform the checks during class construction, and within any accessors. The $type_name argument must be a string. The string may be either a class name or a type defined using Moose's type definition features. (Refer to Moose::Util::TypeConstraints for information on how to define a new type, and how to retrieve type meta-data). coerce => (1|0) This will attempt to use coercion with the supplied type constraint to change the value passed into any accessors or constructors. You must have supplied a type constraint in order for this to work. See Moose::Cookbook::Basics::Recipe5 for an example. does => $role_name This will accept the name of a role which the value stored in this attribute is expected to have consumed. required => (1|0) This marks the attribute as being required. This means a defined value must be supplied during class construction, and the attribute may never be set to undef with an accessor. weak_ref => (1|0) This will tell the class to store the value of this attribute as a weakened reference. If an attribute is a weakened reference, it cannot also be coerced. lazy => (1|0) This will tell the class to not create this slot until absolutely necessary. If an attribute is marked as lazy it must have a default supplied. auto_deref => (1|0) This tells the accessor whether to automatically dereference the value returned. This is only legal if your isa option is either ArrayRef or HashRef . trigger => $code The trigger option is a CODE reference which will be called after the value of the attribute is set. The CODE ref will be passed the instance itself, the updated value and the attribute meta-object (this is for more advanced fiddling and can typically be ignored). You cannot have a trigger on a read-only attribute. handles => ARRAY | HASH | REGEXP | ROLE | CODE The handles option provides Moose classes with automated delegation features. This is a pretty complex and powerful option. It accepts many different option formats, each with its own benefits and drawbacks. NOTE: The class being delegated to does not need to be a Moose based class, which is why this feature is especially useful when wrapping non-Moose classes. All handles option formats share the following traits: You cannot override a locally defined method with a delegated method; an exception will be thrown if you try. That is to say, if you define foo in your class, you cannot override it with a delegated foo . This is almost never something you would want to do, and if it is, you should do it by hand and not use Moose. You cannot override any of the methods found in Moose::Object, or the BUILD and DEMOLISH methods. These will not throw an exception, but will silently move on to the next method in the list. My reasoning for this is that you would almost never want to do this, since it usually breaks your class. As with overriding locally defined methods, if you do want to do this, you should do it manually, not with Moose. You do not need to have a reader (or accessor) for the attribute in order to delegate to it. Moose will create a means of accessing the value for you, however this will be several times less efficient then if you had given the attribute a reader (or accessor) to use. Below is the documentation for each option format: ARRAY This is the most common usage for handles. You basically pass a list of method names to be delegated, and Moose will install a delegation method for each one. HASH This is the second most common usage for handles. Instead of a list of method names, you pass a HASH ref where each key is the method name you want installed locally, and its value is the name of the original method in the class being delegated to. This can be very useful for recursive classes like trees. Here is a quick example (soon to be expanded into a Moose::Cookbook recipe): package Tree; use Moose; has 'node' => (is => 'rw', isa => 'Any'); has 'children' => ( is => 'ro', isa => 'ArrayRef', default => sub { [] } ); has 'parent' => ( is => 'rw', isa => 'Tree', weak_ref => 1, handles => { parent_node => 'node', siblings => 'children', } ); In this example, the Tree package gets parent_node and siblings methods, which delegate to the node and children methods (respectively) of the Tree instance stored in the parent slot. REGEXP The regexp option works very similar to the ARRAY option, except that it builds the list of methods for you. It starts by collecting all possible methods of the class being delegated to, then filters that list using the regexp supplied here. NOTE: An isa option is required when using the regexp option format. This is so that we can determine (at compile time) the method list from the class. Without an isa this is just not possible. ROLE With the role option, you specify the name of a role whose "interface" then becomes the list of methods to handle. The "interface" can be defined as; the methods of the role and any required methods of the role. It should be noted that this does not include any method modifiers or generated attribute methods (which is consistent with role composition). CODE This is the option to use when you really want to do something funky. You should only use it if you really know what you are doing, as it involves manual metaclass twiddling. This takes a code reference, which should expect two arguments. The first is the attribute meta-object this handles is attached to. The second is the metaclass of the class being delegated to. It expects you to return a hash (not a HASH ref) of the methods you want mapped. metaclass => $metaclass_name This tells the class to use a custom attribute metaclass for this particular attribute. Custom attribute metaclasses are useful for extending the capabilities of the has keyword: they are the simplest way to extend the MOP, but they are still a fairly advanced topic and too much to cover here, see Moose::Cookbook::Meta::Recipe1 for more information. The default behavior here is to just load $metaclass_name ; however, we also have a way to alias to a shorter name. This will first look to see if Moose::Meta::Attribute::Custom::$metaclass_name exists. If it does, Moose will then check to see if that has the method register_implementation , which should return the actual name of the custom attribute metaclass. If there is no register_implementation method, it will fall back to using Moose::Meta::Attribute::Custom::$metaclass_name as the metaclass name. traits => [ @role_names ] This tells Moose to take the list of @role_names and apply them to the attribute meta-object. This is very similar to the metaclass option, but allows you to use more than one extension at a time. See "TRAIT NAME RESOLUTION" for details on how a trait name is resolved to a class name. Also see Moose::Cookbook::Meta::Recipe3 for a metaclass trait example. has +$name => %options This is variation on the normal attibute creator has which allows you to clone and extend an attribute from a superclass or from a role. Here is an example of the superclass usage: package Foo; use Moose; has 'message' => ( is => 'rw', isa => 'Str', default => 'Hello, I am a Foo' ); package My::Foo; use Moose; extends 'Foo'; has '+message' => (default => 'Hello I am My::Foo'); What is happening here is that My::Foo is cloning the message attribute from its parent class Foo, retaining the is => 'rw' and isa => 'Str' characteristics, but changing the value in default . Here is another example, but within the context of a role: package Foo::Role; use Moose::Role; has 'message' => ( is => 'rw', isa => 'Str', default => 'Hello, I am a Foo' ); package My::Foo; use Moose; with 'Foo::Role'; has '+message' => (default => 'Hello I am My::Foo'); In this case, we are basically taking the attribute which the role supplied and altering it within the bounds of this feature. Aside from where the attributes come from (one from superclass, the other from a role), this feature works exactly the same. This feature is restricted somewhat, so as to try and force at least some sanity into it. You are only allowed to change the following attributes: default Change the default value of an attribute. coerce Change whether the attribute attempts to coerce a value passed to it. required Change if the attribute is required to have a value. documentation Change the documentation string associated with the attribute. lazy Change if the attribute lazily initializes the slot. isa You are allowed to change the type without restriction. It is recommended that you use this freedom with caution. We used to only allow for extension only if the type was a subtype of the parent's type, but we felt that was too restrictive and is better left as a policy descision. handles You are allowed to add a new handles definition, but you are not allowed to change one. builder You are allowed to add a new builder definition, but you are not allowed to change one. metaclass You are allowed to add a new metaclass definition, but you are not allowed to change one. traits You are allowed to add additional traits to the traits definition. These traits will be composed into the attribute, but pre-existing traits are not overridden, or removed. before $name|@names => sub { ... } after $name|@names => sub { ... } around $name|@names => sub { ... } This three items are syntactic sugar for the before, after, and around method modifier features that Class::MOP provides. More information on these may be found in the Class::MOP::Class documentation for now. super The keyword super is a no-op when called outside of an override method. In the context of an override method, it will call the next most appropriate superclass method with the same arguments as the original method. override ($name, &sub) An override method is a way of explicitly saying "I am overriding this method from my superclass". You can call super within this method, and it will work as expected. The same thing can be accomplished with a normal method call and the SUPER:: pseudo-package; it is really your choice. inner The keyword inner , much like super , is a no-op outside of the context of an augment method. You can think of inner as being the inverse of super ; the details of how inner and augment work is best described in the Moose::Cookbook::Basics::Recipe6. augment ($name, &sub) An augment method, is a way of explicitly saying "I am augmenting this method from my superclass". Once again, the details of how inner and augment work is best described in the Moose::Cookbook::Basics::Recipe6. confess This is the Carp::confess function, and exported here because I use it all the time. blessed This is the Scalar::Util::blessed function, it is exported here because I use it all the time. It is highly recommended that this is used instead of ref anywhere you need to test for an object's class name.

METACLASS TRAITS

When you use Moose, you can also specify traits which will be applied to your metaclass:

use Moose -traits => 'My::Trait';

This is very similar to the attribute traits feature. When you do this, your class's meta object will have the specified traits applied to it. See "TRAIT NAME RESOLUTION" for more details.

TRAIT NAME RESOLUTION

By default, when given a trait name, Moose simply tries to load a class of the same name. If such a class does not exist, it then looks for for a class matching Moose::Meta::$type::Custom::Trait::$trait_name. The $type variable here will be one of Attribute or Class, depending on what the trait is being applied to.

If a class with this long name exists, Moose checks to see if it has the method register_implementation . This method is expected to return the real class name of the trait. If there is no register_implementation method, it will fall back to using Moose::Meta::$type::Custom::Trait::$trait as the trait name.

If all this is confusing, take a look at Moose::Cookbook::Meta::Recipe3, which demonstrates how to create an attribute trait.

UNIMPORTING FUNCTIONS

unimport

Moose offers a way to remove the keywords it exports, through the unimport method. You simply have to say no Moose at the bottom of your code for this to work. Here is an example:

package Person; use Moose; has 'first_name' => (is => 'rw', isa => 'Str'); has 'last_name' => (is => 'rw', isa => 'Str'); sub full_name { my $self = shift; $self->first_name . ' ' . $self->last_name } no Moose; # keywords are removed from the Person package

EXTENDING AND EMBEDDING MOOSE

Moose also offers some options for extending or embedding it into your own framework. To learn more about extending Moose, we recommend checking out the "Extending" recipes in the Moose::Cookbook, starting with Moose::Cookbook::Extending::Recipe1, which provides an overview of all the different ways you might extend Moose.

Moose->init_meta(for_class => $class, base_class => $baseclass, metaclass => $metaclass)

The init_meta method sets up the metaclass object for the class specified by for_class . This method injects a a meta accessor into the class so you can get at this object. It also sets the class's superclass to base_class , with Moose::Object as the default.

You can specify an alternate metaclass with the metaclass parameter.

For more detail on this topic, see Moose::Cookbook::Extending::Recipe2.

This method used to be documented as a function which accepted positional parameters. This calling style will still work for backwards compatibility, but is deprecated.

import

Moose's import method supports the Sub::Exporter form of {into => $pkg} and {into_level => 1} .

NOTE: Doing this is more or less deprecated. Use Moose::Exporter instead, which lets you stack multiple Moose.pm -alike modules sanely. It handles getting the exported functions into the right place for you.

CAVEATS

It should be noted that super and inner cannot be used in the same method. However, they may be combined within the same class hierarchy; see t/014_override_augment_inner_super.t for an example. The reason for this is that super is only valid within a method with the override modifier, and inner will never be valid within an override method. In fact, augment will skip over any override methods when searching for its appropriate inner . This might seem like a restriction, but I am of the opinion that keeping these two features separate (yet interoperable) actually makes them easy to use, since their behavior is then easier to predict. Time will tell whether I am right or not (UPDATE: so far so good).

ACKNOWLEDGEMENTS

I blame Sam Vilain for introducing me to the insanity that is meta-models. I blame Audrey Tang for then encouraging my meta-model habit in #perl6. Without Yuval "nothingmuch" Kogman this module would not be possible, and it certainly wouldn't have this name ;P The basis of the TypeContraints module was Rob Kinyon's idea originally, I just ran with it. Thanks to mst & chansen and the whole #moose posse for all the early ideas/feature-requests/encouragement/bug-finding. Thanks to David "Theory" Wheeler for meta-discussions and spelling fixes.

SEE ALSO

http://www.iinteractive.com/moose This is the official web home of Moose, it contains links to our public SVN repo as well as links to a number of talks and articles on Moose and Moose related technologies. Moose::Cookbook - How to cook a Moose The Moose is flying, a tutorial by Randal Schwartz Part 1 - http://www.stonehenge.com/merlyn/LinuxMag/col94.html Part 2 - http://www.stonehenge.com/merlyn/LinuxMag/col95.html Class::MOP documentation The #moose channel on irc.perl.org The Moose mailing list - moose@perl.org Moose stats on ohloh.net - http://www.ohloh.net/projects/moose Several Moose extension modules in the MooseX:: namespace. See http://search.cpan.org/search?query=MooseX:: for extensions.

Books

The Art of the MetaObject Protocol I mention this in the Class::MOP docs too, this book was critical in the development of both modules and is highly recommended.

Papers

http://www.cs.utah.edu/plt/publications/oopsla04-gff.pdf This paper (suggested by lbr on #moose) was what lead to the implementation of the super / override and inner / augment features. If you really want to understand them, I suggest you read this.

BUGS

All complex software has bugs lurking in it, and this module is no exception. If you find a bug please either email me, or add the bug to cpan-RT.

FEATURE REQUESTS

We are very strict about what features we add to the Moose core, especially the user-visible features. Instead we have made sure that the underlying meta-system of Moose is as extensible as possible so that you can add your own features easily. That said, occasionally there is a feature needed in the meta-system to support your planned extension, in which case you should either email the mailing list or join us on irc at #moose to discuss.

AUTHOR

Stevan Little <stevan@iinteractive.com>

with contributions from:

Aankhen

Adam (Alias) Kennedy

Anders (Debolaz) Nor Berle

Nathan (kolibre) Gray

Christian (chansen) Hansen

Hans Dieter (confound) Pearcey

Eric (ewilhelm) Wilhelm

Guillermo (groditi) Roditi

Jess (castaway) Robinson

Matt (mst) Trout

Robert (phaylon) Sedlacek

Robert (rlb3) Boone

Scott (konobi) McWhirter

Shlomi (rindolf) Fish

Yuval (nothingmuch) Kogman

Chris (perigrin) Prather

Wallace (wreis) Reis

Jonathan (jrockway) Rockway

Dave (autarch) Rolsky

Piotr (dexter) Roszatycki

Sam (mugwump) Vilain

Shawn (sartak) Moore

... and many other #moose folks

COPYRIGHT AND LICENSE

Copyright 2006-2008 by Infinity Interactive, Inc.

http://www.iinteractive.com

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.