Moose(3) User Contributed Perl Documentation Moose(3)NAMEMoose - A postmodern object system for Perl 5
VERSION
version 2.1005
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);
};
DESCRIPTIONMoose 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, 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>.
The source POD files can be found in GitHub:
<http://github.com/jpa/Moose-Doc-JA>
BUILDING CLASSES WITH MOOSEMoose 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 METHODSMoose 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 FUNCTIONSMoose 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, then "extends" tries to load
them.
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|0)
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::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 that
c<required> does not say anything about the attribute's value,
which can be "undef".
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. 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 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::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 the builder option docs in Class::MOP::Attribute and/or
Moose::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 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 ($name, &sub)
An "augment" method, is a way of explicitly saying "I am augmenting
this method from my superclass". Once again, the details of how
"inner" and "augment" work is best described in the
Moose::Cookbook::Basics::Document_AugmentAndInner.
inner
The keyword "inner", much like "super", is a no-op outside of the
context of an "augment" method. You can think of "inner" as being
the inverse of "super"; the details of how "inner" and "augment"
work is best described in the
Moose::Cookbook::Basics::Document_AugmentAndInner.
blessed
This is the "Scalar::Util::blessed" function. It is highly
recommended that this is used instead of "ref" anywhere you need to
test for an object's class name.
confess
This is the "Carp::confess" function, and exported here for
historical reasons.
METACLASS
When you use Moose, you can specify traits which will be applied to
your metaclass:
use Moose-traits => 'My::Trait';
This is very similar to the attribute traits feature. When you do this,
your class's "meta" object will have the specified traits applied to
it. See "Metaclass and Trait Name Resolution" for more details.
Metaclass and Trait Name Resolution
By default, when given a trait name, Moose simply tries to load a class
of the same name. If such a class does not exist, it then looks for a
class matching Moose::Meta::$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::Labeled_AttributeTrait, 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::ExtensionOverview, 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 <mailto:moose@perl.org>. You must be subscribed to
send a message. To subscribe, send an empty message to
<mailto: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.
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
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 manual
This is an introduction to Moose which covers most of the basics.
Modern Perl, by chromatic
This is an introduction to modern Perl programming, which includes
a section on Moose. It is available in print and as a free download
from <http://onyxneon.com/books/modern_perl/>.
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>
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>
Karen (ether) Etheridge <ether@cpan.org>
CONTRIBUTORSMoose 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 in Moose::Manual.
John (jgoulah) Goulah wrote Moose::Cookbook::Snack::Keywords.
Jess (castaway) Robinson wrote Moose::Cookbook::Snack::Types.
Aran (bluefeet) Clary Deltac wrote
Moose::Cookbook::Basics::Genome_OverloadingSubtypesAndCoercion.
Anders (Debolaz) Nor Berle contributed Test::Moose and Moose::Util.
Also, the code in Moose::Meta::Attribute::Native is based on code from
the MooseX::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
Paul (frodwith) Driver
Piotr (dexter) Roszatycki
Robert Buels
Robert (phaylon) Sedlacek
Robert (rlb3) Boone
Sam (mugwump) Vilain
Scott (konobi) McWhirter
Shlomi (rindolf) Fish
Tom (dec) Lanyon
Wallace (wreis) Reis
... and many other #moose folks
AUTHORMoose 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) 2013 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 v5.18.1 2013-08-07 Moose(3)
