Moose - A postmodern object system for Perl 5 |
Moose - A postmodern object system for Perl 5
version 2.1605
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); };
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 the Class::MOP manpage, 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.
If you're new to Moose, the best place to start is the the Moose::Manual manpage docs, followed by the the Moose::Cookbook manpage. 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.
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 (https://metacpan.org/search?q=MooseX::),
or to examine the Task::Moose manpage which aims to keep an up-to-date, easily
installable list of Moose extensions.
Much of the Moose documentation has been translated into other languages.
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
the Moose::Object manpage, 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
the Moose::Object manpage) this includes properly initializing all instance slots,
setting defaults where appropriate, and performing any type constraint checking
or coercion.
Moose provides a number of methods to all your classes, mostly through the
inheritance of the Moose::Object manpage. There is however, one exception. By default,
Moose will install a method named meta
in any class which uses
Moose
. 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, the the Moose::Object manpage class also provides a method named meta
which does the same thing. If your class inherits from the Moose::Object manpage (which
is the default), then you will still have a meta
method. However, if your
class inherits from a parent which provides a meta
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 pass
undef
as the -meta_name
option:
use Moose -meta_name => undef;
Again, you will still inherit meta
from the Moose::Object manpage in this case.
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.
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
/use parent
, 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 the Moose::Object manpage.
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.
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.
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 the Moose::Meta::Attribute manpage (which inherits from the Class::MOP::Attribute manpage),
so the full documentation for the valid options can be found there. These are
the most commonly used options:
$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 the Class::MOP::Attribute manpage, however if you use those, you won't need the is option.
$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 the Moose::Util::TypeConstraints manpage
for information on how to define a new type, and how to retrieve type meta-data).
required
does not
say anything about the attribute's value, which can be undef
.
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.
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
HASH
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
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
DUCKTYPE
duck_type
to create a duck type object. For more
information on duck_type
please check
the Moose::Util::TypeConstraints manpage.
CODE
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.
@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 the Moose::Cookbook::Meta::Labeled_AttributeTrait manpage for a metaclass trait example.
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.
Note that the predicate will return true even for a weak_ref
attribute
whose value has expired.
<
$attr-
documentation >>.
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:
traits
definition.
These traits will be composed into the attribute, but preexisting traits
are not overridden, or removed.
These three items are syntactic sugar for the before, after, and around method modifier features that the Class::MOP manpage provides. More information on these may be found in the Moose::Manual::MethodModifiers manpage and the Class::MOP::Class documentation.
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.
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.
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
the Moose::Cookbook::Basics::Document_AugmentAndInner manpage.
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 the Moose::Cookbook::Basics::Document_AugmentAndInner manpage.
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.
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 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 the Moose::Cookbook::Meta::Labeled_AttributeTrait manpage, which demonstrates how to create an attribute trait.
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
To learn more about extending Moose, we recommend checking out the ``Extending'' recipes in the the Moose::Cookbook manpage, starting with the Moose::Cookbook::Extending::ExtensionOverview manpage, which provides an overview of all the different ways you might extend Moose. the Moose::Exporter manpage and the Moose::Util::MetaRole manpage are the modules which provide the majority of the extension functionality, so reading their documentation should also be helpful.
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 the Class::MOP manpage 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 the Class::MOP manpage 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.
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).
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.
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!
Part 2 - http://www.stonehenge.com/merlyn/LinuxMag/col95.html
MooseX::
namespace.
super
/override
and inner
/augment
features. If you really
want to understand them, I suggest you read this.
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 submit a TODO
test as a
pull request at https://github.com/moose/Moose.
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.
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 the Moose::Manual::Contributing manpage has more detail about how and when you can contribute.
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
.
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 the Moose::Manual manpage.
John (jgoulah) Goulah wrote the Moose::Cookbook::Snack::Keywords manpage.
Jess (castaway) Robinson wrote the Moose::Cookbook::Snack::Types manpage.
Aran (bluefeet) Clary Deltac wrote the Moose::Cookbook::Basics::Genome_OverloadingSubtypesAndCoercion manpage.
Anders (Debolaz) Nor Berle contributed the Test::Moose manpage and the Moose::Util manpage.
Also, the code in the Moose::Meta::Attribute::Native manpage is based on code from the the MooseX::AttributeHelpers manpage 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
This software is copyright (c) 2006 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.
Moose - A postmodern object system for Perl 5 |