NAME¶
Moose - A postmodern object system for Perl 5
VERSION¶
version 2.0603
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, 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|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 ($name, &sub)
- An "augment" method, is a way of explicitly
saying "I am augmenting this method from my superclass". Once
again, the details of how "inner" and "augment" work
is best described in the
Moose::Cookbook::Basics::Document_AugmentAndInner.
- inner
- The keyword "inner", much like "super",
is a no-op outside of the context of an "augment" method. You
can think of "inner" as being the inverse of "super";
the details of how "inner" and "augment" work is best
described in the Moose::Cookbook::Basics::Document_AugmentAndInner.
- blessed
- This is the "Scalar::Util::blessed" function. It
is highly recommended that this is used instead of "ref"
anywhere you need to test for an object's class name.
- confess
- This is the "Carp::confess" function, and
exported here for historical reasons.
When you use Moose, you can specify traits which will be applied to your
metaclass:
use Moose -traits => 'My::Trait';
This is very similar to the attribute traits feature. When you do this, your
class's "meta" object will have the specified traits applied to it.
See "Metaclass and Trait Name Resolution" for more details.
By default, when given a trait name, Moose simply tries to load a class of the
same name. If such a class does not exist, it then looks for for a class
matching
Moose::Meta::$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::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 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 <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.
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
<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¶
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 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
AUTHOR¶
Moose 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) 2012 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.