Moose - A complete modern object system for Perl 5
package Point; use strict; use warnings; use Moose; 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 strict; use warnings; 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.
Yes, I know there has been an explosion recently of new ways to build object's in Perl 5, most of them based on inside-out objects and other such things. Moose is different because it is not a new object system for Perl 5, but instead an extension of the existing object system.
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 also provides the power of metaclass programming.
Moose is based on the prototypes and experiments I did for the Perl 6 meta-model; however Moose is NOT an experiment/prototype, it is for real.
Yes, I believe that it is.
I have two medium-to-large-ish web applications which use Moose heavily and have been in production (without issue) for several months now. At $work, we are re-writing our core offering in it. And several people on #moose have been using it (in production) for several months now as well.
Of course, in the end, you need to make this call yourself. If you have any questions or concerns, please feel free to email me, or even the list or just stop by #moose and ask away.
No. While Moose is very much inspired by Perl 6, it is not itself Perl 6. Instead, it is an OO system for Perl 5. I built Moose because I was tired or writing the same old boring Perl 5 OO code, and drooling over Perl 6 OO. So instead of switching to Ruby, I wrote 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.
Unless specified with extends, any class which uses Moose will inherit from Moose::Object.
extends
Moose will also manage all attributes (including inherited ones) that are defined with has. And assuming that you call new, which is inherited from Moose::Object, then this includes properly initializing all instance slots, setting defaults where appropriate, and performing any type constraint checking or coercion.
has
new
Moose will export a number of functions into the class's namespace which can then be used to set up the class. These functions all work directly on the current class.
This is a method which provides access to the current class's metaclass.
This function will set the superclass(es) for the current class.
This approach is recommended instead of use base, because use base actually pushes 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.
use base
push
@ISA
This will apply a given set of @roles to the local class. Role support is currently under heavy development; see Moose::Role for more details.
@roles
This will install an attribute of a given $name into the current class. The list of %options are the same as those provided by Class::MOP::Attribute, in addition to the list below which are provided by Moose (Moose::Meta::Attribute to be more specific):
$name
%options
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.
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 can be either a class name or a type defined using Moose's type definition features.
$type_name
This will attempt to use coercion with the supplied type constraint to change the value passed into any accessors or constructors. You must have supplied a type constraint in order for this to work. See Moose::Cookbook::Recipe5 for an example usage.
This will accept the name of a role which the value stored in this attribute is expected to have consumed.
This marks the attribute as being required. This means a value must be supplied during class construction, and the attribute can never be set to undef with an accessor.
undef
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.
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 supplied.
This tells the accessor whether to automatically dereference the value returned. This is only legal if your isa option is either an ArrayRef or HashRef.
isa
ArrayRef
HashRef
This tells the class to use a custom attribute metaclass for this particular attribute. Custom attribute metaclasses 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. I will try and write a recipe on it soon.
The default behavior here is to just load $metaclass_name, however, we also have a way to alias to a shorter name. This will first look to see if Moose::Meta::Attribute::Custom::$metaclass_name exists, if it does it will then check to see if that has the method register_implemenetation which should return the actual name of the custom attribute metaclass. If there is no register_implemenetation method, it will just default to using Moose::Meta::Attribute::Custom::$metaclass_name as the metaclass name.
$metaclass_name
register_implemenetation
The trigger option is a CODE reference which will be called after the value of the attribute is set. The CODE ref will be passed the instance itself, the updated value and the attribute meta-object (this is for more advanced fiddling and can typically be ignored in most cases). You cannot have a trigger on a read-only attribute.
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 it's own benefits and drawbacks.
NOTE: This features is no longer experimental, but it still may have subtle bugs lurking in the deeper corners. So if you think you have found a bug, you probably have, so please report it to me right away.
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. Meaning, 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.
foo
You cannot override any of the methods found in Moose::Object as well as BUILD or 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 because it usually tends to break your class. And as with overriding locally defined methods, if you do want to do this, you should do it manually and not with Moose.
BUILD
DEMOLISH
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 in the list.
HASH
This is the second most common usage for handles. Instead of a list of method names, you pass a HASH ref where the key is the method name you want installed locally, and the value is the name of the original method in the class being delegated too.
This can be very useful for recursive classes like trees, here is a quick example (soon to be expanded into a Moose::Cookbook::Recipe):
pacakge Tree; use Moose; has 'node' => (is => 'rw', isa => 'Any'); has 'children' => ( is => 'ro', isa => 'ArrayRef', default => sub { [] } ); has 'parent' => ( is => 'rw', isa => 'Tree', is_weak_ref => 1, handles => { parent_node => 'node', siblings => 'children', } );
In this example, the Tree package gets the parent_node and siblings methods which delegate to the node and children methods of the Tree instance stored in the parent slot.
parent_node
siblings
node
children
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 too, 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.
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 too. The second is the metaclass of the class being delegated too. It expects you to return a hash (not a HASH ref) of the methods you want mapped.
This is variation on the normal attibute creator has, which allows you to clone and extend an attribute from a superclass. Here is a quick example:
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 it's parent class Foo, retaining the is => 'rw' and isa => 'Str' characteristics, but changing the value in default.
message
default
This feature is restricted somewhat, so as to try and enfore at least some sanity into it. You are only allowed to change the following attributes:
Change the default value of an attribute.
Change whether the attribute attempts to coerce a value passed to it.
Change if the attribute is required to have a value.
Change the documentation string associated with the attribute.
You are allowed to change the type, but if and only if the new type is a subtype of the old type.
This three items are syntactic sugar for the before, after, and around method modifier features that Class::MOP provides. More information on these can be found in the Class::MOP documentation for now.
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.
super
override
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 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.
inner
augment
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.
This is the Carp::confess function, and exported here because I use it all the time. This feature may change in the future, so you have been warned.
Carp::confess
This is the Scalar::Uti::blessed function, it is exported here because I use it all the time. It is highly recommended that this is used instead of ref anywhere you need to test for an object's class name.
Scalar::Uti::blessed
ref
Moose offers a way of removing the keywords it exports though the unimport method. You simply have to say no Moose at the bottom of your code for this to work. Here is an example:
unimport
no Moose
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
Moose doesn't stand for one thing in particular, however, if you want, here are a few of my favorites; feel free to contribute more :)
It should be noted that super and inner cannot be used in the same method. However, they can be combined together with the same class hierarchy; see t/014_override_augment_inner_super.t for an example.
cannot
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 (but interoperable) actually makes them easy to use, since their behavior is then easier to predict. Time will tell if I am right or not.
This paper (suggested by lbr on #moose) was what lead to the implementation of the super/overrride and inner/augment features. If you really want to understand this feature, I suggest you read this.
overrride
All complex software has bugs lurking in it, and this module is no exception. If you find a bug please either email me, or add the bug to cpan-RT.
Stevan Little <stevan@iinteractive.com>
Christian Hansen <chansen@cpan.org>
Yuval Kogman <nothingmuch@woobling.org>
Copyright 2006, 2007 by Infinity Interactive, Inc.
http://www.iinteractive.com
This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.
To install Moose, copy and paste the appropriate command in to your terminal.
cpanm
cpanm Moose
CPAN shell
perl -MCPAN -e shell install Moose
For more information on module installation, please visit the detailed CPAN module installation guide.