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Moose(3)                             User Contributed Perl Documentation                            Moose(3)



NAME
       Moose - A postmodern object system for Perl 5

VERSION
       version 2.0205

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 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::Manual 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, upto-date,
       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 at http://perldoc.perlassociation.org/pod/Moose-Doc-JA/index.html
           <http://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 <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 you "use Moose", Moose will set the class's parent class to Moose::Object, unless the class
       using Moose already has a parent class. In addition, specifying a parent with "extends" will change
       the parent class.

       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.

       meta
           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.

           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 with "extends", 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.

       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 for Moose::Meta::Attribute (which inherits from Class::MOP::Attribute),
           so the full documentation for the valid options can be found there. These are the most commonly
           used options:

           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|_)
               This will attempt to use coercion with the supplied type constraint to change the value
               passed into any accessors or constructors. You must supply a type constraint, and that type
               constraint must define a coercion. 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|_)
               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 that
               c<required> does not say anything about the attribute's value, which can be "undef".

           weak_ref => (1|_)
               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. 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|_)
               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 or builder supplied.

           trigger => $code
               The trigger 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.

               You can have a trigger on a read-only attribute.

               NOTE: Triggers will only fire when you assign to the attribute, either in the constructor, or
               using the writer. Default and built values will not cause the trigger to be fired.

           handles => ARRAY | HASH | REGEXP | ROLE | ROLETYPE | DUCKTYPE | 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.

                   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: 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" or "ROLETYPE"
                   With the role option, you specify the name of a role or a role 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
                   does not 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
                   to "duck_type" to create a duck type object. For more information on "duck_type" please
                   check Moose::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 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.

           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 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 "Metaclass and Trait Name Resolution" for details on how a trait name is resolved to a
               role name.

               Also see Moose::Cookbook::Meta::Recipe3 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 the builder option docs in Class::MOP::Attribute and/or
               Moose::Cookbook::Basics::Recipe8 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 the default option docs in Class::MOP::Attribute for more
               information.

           clearer => Str
               Creates a method allowing you to clear the value. See the clearer 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
               the predicate option docs in Class::MOP::Attribute for more information.

               Note that the predicate will return true even for a "weak_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 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.

           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
           least some 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 to add additional traits to the "traits" definition.  These traits will be
               composed into the attribute, but preexisting traits are 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
           that Class::MOP provides. More information on these may be found in
           Moose::Manual::MethodModifiers and the Class::MOP::Class documentation.

       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.

       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.

       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.

       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.

       blessed
           This is the "Scalar::Util::blessed" function. It is highly recommended that this is used instead
           of "ref" anywhere you need to test for an object's class name.

       confess
           This is the "Carp::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's "meta" object
       will have the specified traits applied to it. See "Metaclass and Trait Name Resolution" for more
       details.

   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 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.

       The lookup method for metaclasses is the same, except that it looks for a class matching
       Moose::Meta::$type::Custom::$metaclass_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
       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::Exporter and Moose::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 extension for Moose itself you'll want to put your extension in the
       "MooseX::" namespace. This namespace is specifically for extensions that make Moose better or
       different in some fundamental way. It is traditionally not for a package that just happens to use
       Moose. This namespace follows from the examples of the "LWPx::" and "DBIx::" namespaces that perform
       the same function for "LWP" and "DBI" respectively.

METACLASS COMPATIBILITY AND MOOSE
       Metaclass compatibility is a thorny subject. You should start by reading the "About Metaclass
       compatibility" section in the "Class::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 that "Class::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 various "MooseX::*" 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 that "super" and "inner" cannot be used in the same method. However, they may
           be combined within the same class hierarchy; see t/basics/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).

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

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

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

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 git repository as well as
           links to a number of talks and articles on Moose and Moose related technologies.

       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>

       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, as 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
       <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.

       Please report any bugs to "bug-moose@rt.cpan.org", or through the web interface at
       <http://rt.cpan.org>.

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

       Stevan (stevan) Little <stevan@iinteractive.com>

       Jesse (doy) Luehrs <doy at tozt dot net>

       Yuval (nothingmuch) Kogman

       Shawn (sartak) Moore <sartak@bestpractical.com>

       Hans Dieter (confound) Pearcey <hdp@pobox.com>

       Chris (perigrin) Prather

       Florian Ragwitz <rafl@debian.org>

       Dave (autarch) Rolsky <autarch@urth.org>

CONTRIBUTORS
       Aankhen

       Adam (Alias) Kennedy

       Anders (Debolaz) Nor Berle

       Chris (perigrin) Prather

       Christian (chansen) Hansen

       Cory (gphat) Watson

       Dylan Hardison (doc fixes)

       Eric (ewilhelm) Wilhelm

       Evan Carroll

       Florian (rafl) Ragwitz

       Guillermo (groditi) Roditi

       Jason May

       Jay Hannah

       Jess (castaway) Robinson

       Jonathan (jrockway) Rockway

       Matt (mst) Trout

       Nathan (kolibrie) Gray

       Paul (frodwith) Driver

       Piotr (dexter) Roszatycki

       Robert Buels

       Robert (phaylon) Sedlacek

       Robert (rlb3) Boone

       Sam (mugwump) Vilain

       Scott (konobi) McWhirter

       Shawn (Sartak) Moore

       Shlomi (rindolf) Fish

       Tom (dec) Lanyon

       Wallace (wreis) Reis

       ... and many other #moose folks

AUTHOR
       Stevan Little <stevan@iinteractive.com>

COPYRIGHT AND LICENSE
       This software is copyright (c) 2011 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.



perl v5.12.5                                     2011-09-06                                         Moose(3)