NAME

Moose - A postmodern object system for Perl 5

VERSION

version 2.2207

SYNOPSIS

package Point;use Moose; # automatically turns on strict and warningshas '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 think more about what you want to do and less about the mechanics of OOP.

Additionally, Moose is built on top ofClass::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 theMoose::Manual docs, followed by theMoose::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

TheMooseX:: 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 (https://metacpan.org/search?q=MooseX::), or to examineTask::Moose which aims to keep an up-to-date, easily installable list of Moose extensions.

TRANSLATIONS

Much of the Moose documentation has been translated into other languages.

Japanese: Japanese docs can be found athttp://perldoc.perlassociation.org/pod/Moose-Doc-JA/index.html. The source POD files can be found in GitHub:http://github.com/jpa/Moose-Doc-JA

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.

When youuse Moose, Moose will set the class's parent class toMoose::Object,unless the class using Moose already has a parent class. In addition, specifying a parent withextends will change the parent class.

Moose will also manage all attributes (including inherited ones) that are defined withhas. And (assuming you callnew, which is inherited fromMoose::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 ofMoose::Object. There is however, one exception. By default, Moose will install a method namedmeta in any class which usesMoose. This method returns the current class's metaclass.

If you'd like to rename this method, you can do so by passing the-meta_name option when using Moose:

use Moose -meta_name => 'my_meta';

However, theMoose::Object classalso provides a method namedmeta which does the same thing. If your class inherits fromMoose::Object (which is the default), then you will still have ameta method. However, if your class inherits from a parent which provides ameta method of its own, your class will inherit that instead.

If you'd like for Moose to not install a meta method at all, you can passundef as the-meta_name option:

use Moose -meta_name => undef;

Again, you will still inheritmeta fromMoose::Object in this case.

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. If the parent classes are not yet loaded, thenextends tries to load them.

This approach is recommended instead ofusebase/useparent, becauseuse base actuallypushes onto the class's@ISA, whereasextends will replace it. This is important to ensure that classes which do not have superclasses still properly inherit fromMoose::Object.

Each superclass can be followed by a hash reference with options. Currently, only-version is recognized:

extends 'My::Parent'      => { -version => 0.01 },        'My::OtherParent' => { -version => 0.03 };

An exception will be thrown if the version requirements are not satisfied.

with (@roles)

This will apply a given set of@roles to the local class.

Like withextends, each specified role can be followed by a hash reference with a-version option:

with 'My::Role'      => { -version => 0.32 },     'My::Otherrole' => { -version => 0.23 };

The specified version requirements must be satisfied, otherwise an exception will be thrown.

If your role takes options or arguments, they can be passed along in the hash reference as well.

You should only use onewith, even if you are consuming multiple roles. If you consume roles using multiplewith statements Moose cannot detect method conflicts between those roles.

has $name|@$names => %options

This will install an attribute of a given$name into the current class. If the first parameter is an array reference, it will create an attribute for every$name in the list. The%options will be passed to the constructor forMoose::Meta::Attribute (which inherits fromClass::MOP::Attribute), so the full documentation for the valid options can be found there. These are the most commonly used options:

is => 'rw'|'ro'

Theis option accepts eitherrw (for read/write) orro (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 thereader,writer andaccessor options inherited fromClass::MOP::Attribute, however if you use those, you won't need theis option.

isa => $type_name

Theisa 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 toMoose::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. Youmust supply a type constraint, and that type constraintmust define a coercion. SeeMoose::Cookbook::Basics::HTTP_SubtypesAndCoercion 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 value must be supplied during class construction,or the attribute must be lazy and have either a default or a builder. Note thatrequired does not say anything about the attribute's value, which can beundef.

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, itcannot also be coerced. Note that when a weak ref expires, the attribute's value becomes undefined, and is still considered to be set for purposes of predicate, default, etc.

lazy => (1|0)

This will tell the class to not create this slot until absolutely necessary. If an attribute is marked as lazy itmust have a default or builder supplied.

trigger => $code

Thetrigger option is a CODE reference which will be called after the value of the attribute is set. The CODE ref is passed the instance itself, the updated value, and the original value if the attribute was already set.

Youcan have a trigger on a read-only attribute.

NOTE: Triggers will only fire when youassign to the attribute, either in the constructor, or using the writer. Default and built values willnot cause the trigger to be fired.

Thehandles 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.

Allhandles 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 definefoo in your class, you cannot override it with a delegatedfoo. 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 theBUILD andDEMOLISH 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 notneed 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 timesless 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 forhandles. 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 forhandles. 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 getsparent_node andsiblings methods, which delegate to thenode andchildren methods (respectively) of the Tree instance stored in theparent slot.

You may also use an array reference to curry arguments to the original method.

has 'thing' => (    ...    handles => { set_foo => [ set => 'foo' ] },);# $self->set_foo(...) calls $self->thing->set('foo', ...)

The first element of the array reference is the original method name, and the rest is a list of curried arguments.

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: Anisa 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 anisa this is just not possible.

ROLE orROLETYPE

With the role option, you specify the name of a role or arole type 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 doesnot include any method modifiers or generated attribute methods (which is consistent with role composition).

DUCKTYPE

With the duck type option, you pass a duck type object whose "interface" then becomes the list of methods to handle. The "interface" can be defined as the list of methods passed toduck_type to create a duck type object. For more information onduck_type please checkMoose::Util::TypeConstraints.

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 thishandles 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.

traits => [ @role_names ]

This tells Moose to take the list of@role_names and apply them to the attribute meta-object. Custom attribute metaclass traits are useful for extending the capabilities of thehas 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"Metaclass and Trait Name Resolution" for details on how a trait name is resolved to a role name.

Also seeMoose::Cookbook::Meta::Labeled_AttributeTrait for a metaclass trait example.

builder => Str

The value of this key is the name of the method that will be called to obtain the value used to initialize the attribute. See thebuilder option docs in Class::MOP::Attribute and/orMoose::Cookbook::Basics::BinaryTree_BuilderAndLazyBuild for more information.

default => SCALAR | CODE

The value of this key is the default value which will initialize the attribute.

NOTE: If the value is a simple scalar (string or number), then it can be just passed as is. However, if you wish to initialize it with a HASH or ARRAY ref, then you need to wrap that inside a CODE reference. See thedefault option docs in Class::MOP::Attribute for more information.

clearer => Str

Creates a method allowing you to clear the value. See theclearer option docs in Class::MOP::Attribute for more information.

predicate => Str

Creates a method to perform a basic test to see if a value has been set in the attribute. See thepredicate option docs in Class::MOP::Attribute for more information.

Note that the predicate will return true even for aweak_ref attribute whose value has expired.

documentation => $string

An arbitrary string that can be retrieved later by calling$attr->documentation.

has +$name => %options

This is variation on the normal attribute creatorhas 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 thatMy::Foo is cloning themessage attribute from its parent classFoo, retaining theis => 'rw' andisa => 'Str' characteristics, but changing the value indefault.

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.

Note that you can only extend an attribute from either a superclass or a role, you cannot extend an attribute in a role that composes over an attribute from another role.

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 leastsome sanity into it. Most options work the same, but there are some exceptions:

reader
writer
accessor
clearer
predicate: These options can be added, but cannot override a superclass definition.
traits: You are allowed toadd additional traits to thetraits definition. These traits will be composed into the attribute, but preexisting traitsare not overridden, or removed.

before $name|@names|\@names|qr/.../ => sub { ... }

after $name|@names|\@names|qr/.../ => sub { ... }

around $name|@names|\@names|qr/.../ => sub { ... }

These three items are syntactic sugar for the before, after, and around method modifier features thatClass::MOP provides. More information on these may be found inMoose::Manual::MethodModifiers and theClass::MOP::Class documentation.

override ($name, &sub)

Anoverride method is a way of explicitly saying "I am overriding this method from my superclass". You can callsuper within this method, and it will work as expected. The same thingcan be accomplished with a normal method call and theSUPER:: pseudo-package; it is really your choice.

super

The keywordsuper is a no-op when called outside of anoverride method. In the context of anoverride method, it will call the next most appropriate superclass method with the same arguments as the original method.

augment ($name, &sub)

Anaugment method, is a way of explicitly saying "I am augmenting this method from my superclass". Once again, the details of howinner andaugment work is best described in theMoose::Cookbook::Basics::Document_AugmentAndInner.

inner

The keywordinner, much likesuper, is a no-op outside of the context of anaugment method. You can think ofinner as being the inverse ofsuper; the details of howinner andaugment work is best described in theMoose::Cookbook::Basics::Document_AugmentAndInner.

blessed

This is theScalar::Util::blessed function. It is highly recommended that this is used instead ofref anywhere you need to test for an object's class name.

confess

This is theCarp::confess function, and exported here for historical reasons.

METACLASS

When you use Moose, you can 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'smeta object will have the specified traits applied to it.

Metaclass and 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 a class matchingMoose::Meta::$type::Custom::Trait::$trait_name. The$type variable here will be one ofAttribute orClass, 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 methodregister_implementation. This method is expected to return thereal class name of the trait. If there is noregister_implementation method, it will fall back to usingMoose::Meta::$type::Custom::Trait::$trait as the trait name.

The lookup method for metaclasses is the same, except that it looks for a class matchingMoose::Meta::$type::Custom::$metaclass_name.

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

UNIMPORTING FUNCTIONS

unimport

Moose offers a way to remove the keywords it exports, through theunimport method. You simply have to sayno 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

To learn more about extending Moose, we recommend checking out the "Extending" recipes in theMoose::Cookbook, starting withMoose::Cookbook::Extending::ExtensionOverview, which provides an overview of all the different ways you might extend Moose.Moose::Exporter andMoose::Util::MetaRole are the modules which provide the majority of the extension functionality, so reading their documentation should also be helpful.

The MooseX:: namespace

Generally if you're writing an extensionfor Moose itself you'll want to put your extension in theMooseX:: namespace. This namespace is specifically for extensions that make Moose better or different in some fundamental way. It is traditionallynot for a package that just happens to use Moose. This namespace follows from the examples of theLWPx:: andDBIx:: namespaces that perform the same function forLWP andDBI respectively.

METACLASS COMPATIBILITY AND MOOSE

Metaclass compatibility is a thorny subject. You should start by reading the "About Metaclass compatibility" section in theClass::MOP docs.

Moose will attempt to resolve a few cases of metaclass incompatibility when you set the superclasses for a class, in addition to the cases thatClass::MOP handles.

Moose tries to determine if the metaclasses only "differ by roles". This means that the parent and child's metaclass share a common ancestor in their respective hierarchies, and that the subclasses under the common ancestor are only different because of role applications. This case is actually fairly common when you mix and match variousMooseX::* modules, many of which apply roles to the metaclass.

If the parent and child do differ by roles, Moose replaces the metaclass in the child with a newly created metaclass. This metaclass is a subclass of the parent's metaclass which does all of the roles that the child's metaclass did before being replaced. Effectively, this means the new metaclass does all of the roles done by both the parent's and child's original metaclasses.

Ultimately, this is all transparent to you except in the case of an unresolvable conflict.

CAVEATS

It should be noted thatsuper andinnercannot be used in the same method. However, they may be combined within the same class hierarchy; seet/basics/override_augment_inner_super.t for an example.

The reason for this is thatsuper is only valid within a method with theoverride modifier, andinner will never be valid within anoverride method. In fact,augment will skip over anyoverride methods when searching for its appropriateinner.

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).

GETTING HELP

We offer both a mailing list and a very active IRC channel.

The mailing list ismailto:moose@perl.org. You must be subscribed to send a message. To subscribe, send an empty message tomailto:moose-subscribe@perl.org

You can also visit us at#moose onirc://irc.perl.org/#moose This channel is quite active, and questions at all levels (on Moose-related topics ;) are welcome.

WHAT DOES MOOSE STAND FOR?

Moose doesn't stand for one thing in particular, however, if you want, here are a few of our favorites. Feel free to contribute more!

Make Other Object Systems Envious
Makes Object Orientation So Easy
Makes Object Orientation Spiffy- Er (sorry ingy)
Most Other Object Systems Emasculate
Moose Often Ovulate Sorta Early
Moose Offers Often Super Extensions
Meta Object Obligates Salivary Excitation
Meta Object Orientation Syntax Extensions
Moo, Only Overengineered, Slow, and Execrable (blame rjbs!)
Massive Object-Oriented Stacktrace Emitter

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.

BUGS

All complex software has bugs lurking in it, and this module is no exception.

Please report any bugs tobug-moose@rt.cpan.org, or through the web interface athttp://rt.cpan.org. You can also submit aTODO test as a pull request athttps://github.com/moose/Moose.

You can also discuss feature requests or possible bugs on the Moose mailing list (moose@perl.org) or on IRC atirc://irc.perl.org/#moose.

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 (moose@perl.org) or join us on IRC atirc://irc.perl.org/#moose to discuss. TheMoose::Manual::Contributing has more detail about how and when you can contribute.

CABAL

There are only a few people with the rights to release a new version of Moose. The Moose Cabal are the people to go to with questions regarding the wider purview of Moose. They help maintain not just the code but the community as well. See the list below under"AUTHORS".

CONTRIBUTORS

Moose is a community project, and as such, involves the work of many, many members of the community beyond just the members in the cabal. In particular:

Dave (autarch) Rolsky wrote most of the documentation inMoose::Manual.

John (jgoulah) Goulah wroteMoose::Cookbook::Snack::Keywords.

Jess (castaway) Robinson wroteMoose::Cookbook::Snack::Types.

Aran (bluefeet) Clary Deltac wroteMoose::Cookbook::Basics::Genome_OverloadingSubtypesAndCoercion.

Anders (Debolaz) Nor Berle contributedTest::Moose andMoose::Util.

Also, the code inMoose::Meta::Attribute::Native is based on code from theMooseX::AttributeHelpers distribution, which had contributions from:

Chris (perigrin) Prather

Cory (gphat) Watson

Evan Carroll

Florian (rafl) Ragwitz

Jason May

Jay Hannah

Jesse (doy) Luehrs

Paul (frodwith) Driver

Robert (rlb3) Boone

Robert Buels

Robert (phaylon) Sedlacek

Shawn (Sartak) Moore

Stevan Little

Tom (dec) Lanyon

Yuval Kogman

Finally, these people also contributed various tests, bug fixes, documentation, and features to the Moose codebase:

Aankhen

Adam (Alias) Kennedy

Christian (chansen) Hansen

Cory (gphat) Watson

Dylan Hardison (doc fixes)

Eric (ewilhelm) Wilhelm

Evan Carroll

Guillermo (groditi) Roditi

Jason May

Jay Hannah

Jonathan (jrockway) Rockway

Matt (mst) Trout

Nathan (kolibrie) Gray