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Matt S Trout > Moo-0.091002 > Moo



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Module Version: 0.091002   Source   Latest Release: Moo-2.003004


Moo - Minimalist Object Orientation (with Moose compatiblity)


 package Cat::Food;

 use Moo;
 use Sub::Quote;

 sub feed_lion {
   my $self = shift;
   my $amount = shift || 1;

   $self->pounds( $self->pounds - $amount );

 has taste => (
   is => 'ro',

 has brand => (
   is  => 'ro',
   isa => sub {
     die "Only SWEET-TREATZ supported!" unless $_[0] eq 'SWEET-TREATZ'

 has pounds => (
   is  => 'rw',
   isa => quote_sub q{ die "$_[0] is too much cat food!" unless $_[0] < 15 },


and else where

 my $full = Cat::Food->new(
    taste  => 'DELICIOUS.',
    brand  => 'SWEET-TREATZ',
    pounds => 10,


 say $full->pounds;


This module is an extremely light-weight, high-performance Moose replacement. It also avoids depending on any XS modules to allow simple deployments. The name Moo is based on the idea that it provides almost -but not quite- two thirds of Moose.

Unlike Mouse this module does not aim at full Moose compatibility. See "INCOMPATIBILITIES" for more details.


If you want a full object system with a rich Metaprotocol, Moose is already wonderful.

I've tried several times to use Mouse but it's 3x the size of Moo and takes longer to load than most of my Moo based CGI scripts take to run.

If you don't want Moose, you don't want "less metaprotocol" like Mouse, you want "as little as possible" - which means "no metaprotocol", which is what Moo provides.

By Moo 1.0 I intend to have Moo's equivalent of Any::Moose built in - if Moose gets loaded, any Moo class or role will act as a Moose equivalent if treated as such.

Hence - Moo exists as its name - Minimal Object Orientation - with a pledge to make it smooth to upgrade to Moose when you need more than minimal features.

Moo and Moose - NEW, EXPERIMENTAL ^

If Moo detects Moose being loaded, it will automatically register metaclasses for your Moo and Moo::Role packages, so you should be able to use them in Moose code without it ever realising you aren't using Moose everywhere.

Extending a Moose class or consuming a Moose::Role should also work.

This means that there is no need for anything like Any::Moose for Moo code - Moo and Moose code should simply interoperate without problem.

However, these features are new as of 0.91.0 (0.091000) so while serviceable, they are absolutely certain to not be 100% yet; please do report bugs.

If you need to disable the metaclass creation, add:

  no Moo::sification;

to your code before Moose is loaded, but bear in mind that this switch is currently global and turns the mechanism off entirely, so don't put this in library code, only in a top level script as a temporary measure while you send a bug report.



 Foo::Bar->new( attr1 => 3 );


 Foo::Bar->new({ attr1 => 3 });


   my ( $class, @args ) = @_;

   unshift @args, "attr1" if @args % 2 == 1;

   return { @args };

 Foo::Bar->new( 3 );

The default implementation of this method accepts a hash or hash reference of named parameters. If it receives a single argument that isn't a hash reference it throws an error.

You can override this method in your class to handle other types of options passed to the constructor.

This method should always return a hash reference of named options.


Define a BUILD method on your class and the constructor will automatically call the BUILD method from parent down to child after the object has been instantiated. Typically this is used for object validation or possibly logging.


If you have a DEMOLISH method anywhere in your inheritance hierarchy, a DESTROY method is created on first object construction which will call $instance->DEMOLISH($in_global_destruction) for each DEMOLISH method from child upwards to parents.

Note that the DESTROY method is created on first construction of an object of your class in order to not add overhead to classes without DEMOLISH methods; this may prove slightly surprising if you try and define your own.


 if ($foo->does('Some::Role1')) {

Returns true if the object composes in the passed role.



 extends 'Parent::Class';

Declares base class. Multiple superclasses can be passed for multiple inheritance (but please use roles instead).

Calling extends more than once will REPLACE your superclasses, not add to them like 'use base' would.


 with 'Some::Role1';
 with 'Some::Role2';

Composes a Role::Tiny into current class. Only one role may be composed in at a time to allow the code to remain as simple as possible.


 has attr => (
   is => 'ro',

Declares an attribute for the class.

The options for has are as follows:


 before foo => sub { ... };

See "before method(s) => sub { ... }" in Class::Method::Modifiers for full documentation.


 around foo => sub { ... };

See "around method(s) => sub { ... }" in Class::Method::Modifiers for full documentation.


 after foo => sub { ... };

See "after method(s) => sub { ... }" in Class::Method::Modifiers for full documentation.


"quote_sub" in Sub::Quote allows us to create coderefs that are "inlineable," giving us a handy, XS-free speed boost. Any option that is Sub::Quote aware can take advantage of this.


You can only compose one role at a time. If your application is large or complex enough to warrant complex composition, you wanted Moose. Note that this does not mean you can only compose one role per class -

  with 'FirstRole';
  with 'SecondRole';

is absolutely fine, there's just currently no equivalent of Moose's

  with 'FirstRole', 'SecondRole';

which composes the two roles together, and then applies them.

There is no built in type system. isa is verified with a coderef, if you need complex types, just make a library of coderefs, or better yet, functions that return quoted subs. MooX::Types::MooseLike provides a similar API to MooseX::Types::Moose so that you can write

  has days_to_live => (is => 'ro', isa => Int);

and have it work with both; it is hoped that providing only subrefs as an API will encourage the use of other type systems as well, since it's probably the weakest part of Moose design-wise.

initializer is not supported in core since the author considers it to be a bad idea but may be supported by an extension in future. Meanwhile trigger or coerce are more likely to be able to fulfill your needs.

There is no meta object. If you need this level of complexity you wanted Moose - Moo succeeds at being small because it explicitly does not provide a metaprotocol.

No support for super, override, inner, or augment - override can be handled by around albeit with a little more typing, and the author considers augment to be a bad idea.

The dump method is not provided by default. The author suggests loading Devel::Dwarn into main:: (via perl -MDevel::Dwarn ... for example) and using $obj->$::Dwarn() instead.

"default" only supports coderefs, because doing otherwise is usually a mistake anyway.

lazy_build is not supported per se, but of course it will work if you manually set all the options it implies.

auto_deref is not supported since the author considers it a bad idea.

documentation is not supported since it's a very poor replacement for POD.

Handling of warnings: when you use Moo we enable FATAL warnings. The nearest similar invocation for Moose would be:

  use Moose;
  use warnings FATAL => "all";

Additionally, Moo supports a set of attribute option shortcuts intended to reduce common boilerplate. The set of shortcuts is the same as in the Moose module MooseX::AttributeShortcuts as of its version 0.009+. So if you:

    package MyClass;
    use Moo;

The nearest Moose invocation would be:

    package MyClass;

    use Moose;
    use warnings FATAL => "all";
    use MooseX::AttributeShortcuts;

or, if you're inheriting from a non-Moose class,

    package MyClass;

    use Moose;
    use MooseX::NonMoose;
    use warnings FATAL => "all";
    use MooseX::AttributeShortcuts;

Finally, Moose requires you to call


at the end of your class to get an inlined (i.e. not horribly slow) constructor. Moo does it automatically the first time ->new is called on your class.


IRC: #web-simple on


mst - Matt S. Trout (cpan:MSTROUT) <>


dg - David Leadbeater (cpan:DGL) <>

frew - Arthur Axel "fREW" Schmidt (cpan:FREW) <>

hobbs - Andrew Rodland (cpan:ARODLAND) <>

jnap - John Napiorkowski (cpan:JJNAPIORK) <>

ribasushi - Peter Rabbitson (cpan:RIBASUSHI) <>

chip - Chip Salzenberg (cpan:CHIPS) <>

ajgb - Alex J. G. Burzyński (cpan:AJGB) <>

doy - Jesse Luehrs (cpan:DOY) <doy at tozt dot net>

perigrin - Chris Prather (cpan:PERIGRIN) <>


Copyright (c) 2010-2011 the Moo "AUTHOR" and "CONTRIBUTORS" as listed above.


This library is free software and may be distributed under the same terms as perl itself.

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