Moo - Minimalist Object Orientation (with Moose compatibility)

      package Cat::Food;

      use Moo;
      use strictures 2;
      use namespace::clean;

      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 => sub { die "$_[0] is too much cat food!" unless $_[0] < 15 },


    And elsewhere:

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


      say $full->pounds;

    "Moo" is an extremely light-weight Object Orientation system. It allows
    one to concisely define objects and roles with a convenient syntax that
    avoids the details of Perl's object system. "Moo" contains a subset of
    Moose and is optimised for rapid startup.

    "Moo" avoids depending on any XS modules to allow for simple
    deployments. The name "Moo" is based on the idea that it provides almost
    -- but not quite -- two thirds of Moose. As such, the Moose::Manual can
    serve as an effective guide to "Moo" aside from the MOP and Types

    Unlike Mouse this module does not aim at full compatibility with Moose's
    surface syntax, preferring instead to provide full interoperability via
    the metaclass inflation capabilities described in "MOO AND MOOSE".

    For a full list of the minor differences between Moose and Moo's surface

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

    But if you don't want to use Moose, you may not want "less metaprotocol"
    like Mouse offers, but you probably want "no metaprotocol", which is
    what Moo provides. "Moo" is ideal for some situations where deployment
    or startup time precludes using Moose and Mouse:

    a command line or CGI script where fast startup is essential
    code designed to be deployed as a single file via App::FatPacker
    a CPAN module that may be used by others in the above situations

    "Moo" maintains transparent compatibility with Moose so if you install
    and load Moose you can use Moo classes and roles in Moose code without

    Moo -- Minimal Object Orientation -- aims to make it smooth to upgrade
    to Moose when you need more than the minimal features offered by Moo.

    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 modification.

    Moo will also create Moose type constraints for Moo classes and roles,
    so that in Moose classes "isa => 'MyMooClass'" and "isa => 'MyMooRole'"
    work the same as for Moose classes and roles.

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

    Extending a Mouse class or consuming a Mouse::Role will also work. But
    note that we don't provide Mouse metaclasses or metaroles so the other
    way around doesn't work. This feature exists for Any::Moose users
    porting to Moo; enabling Mouse users to use Moo classes is not a
    priority for us.

    This means that there is no need for anything like Any::Moose for Moo
    code - Moo and Moose code should simply interoperate without problem. To
    handle Mouse code, you'll likely need an empty Moo role or class
    consuming or extending the Mouse stuff since it doesn't register true
    Moose metaclasses like Moo does.

    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 global and turns the mechanism off entirely so don't put this in
    library code.

    If a new enough version of Class::XSAccessor is available, it will be
    used to generate simple accessors, readers, and writers for better
    performance. Simple accessors are those without lazy defaults, type
    checks/coercions, or triggers. Simple readers are those without lazy
    defaults. Readers and writers generated by Class::XSAccessor will behave
    slightly differently: they will reject attempts to call them with the
    incorrect number of parameters.

    Any::Moose will load Mouse normally, and Moose in a program using Moose
    - which theoretically allows you to get the startup time of Mouse
    without disadvantaging Moose users.

    Sadly, this doesn't entirely work, since the selection is load order
    dependent - Moo's metaclass inflation system explained above in "MOO AND
    MOOSE" is significantly more reliable.

    So if you want to write a CPAN module that loads fast or has only pure
    perl dependencies but is also fully usable by Moose users, you should be
    using Moo.

    For a full explanation, see the article
    <> which
    explains the differing strategies in more detail and provides a direct
    example of where Moo succeeds and Any::Moose fails.

    Moo provides several methods to any class using it.

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


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

    The constructor for the class. By default it will accept attributes
    either as a hashref, or a list of key value pairs. This can be
    customized with the "BUILDARGS" method.

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

    Returns true if the object composes in the passed role.

      if ($foo->DOES('Some::Role1') || $foo->DOES('Some::Class1')) {

    Similar to "does", but will also return true for both composed roles and

      my $meta = Foo::Bar->meta;
      my @methods = $meta->get_method_list;

    Returns an object that will behave as if it is a Moose metaclass object
    for the class. If you call anything other than "make_immutable" on it,
    the object will be transparently upgraded to a genuine
    Moose::Meta::Class instance, loading Moose in the process if required.
    "make_immutable" itself is a no-op, since we generate metaclasses that
    are already immutable, and users converting from Moose had an
    unfortunate tendency to accidentally load Moose by calling it.

    There are several methods that you can define in your class to control
    construction and destruction of objects. They should be used rather than
    trying to modify "new" or "DESTROY" yourself.

      around BUILDARGS => sub {
        my ( $orig, $class, @args ) = @_;

        return { attr1 => $args[0] }
          if @args == 1 && !ref $args[0];

        return $class->$orig(@args);

      Foo::Bar->new( 3 );

    This class method is used to transform the arguments to "new" into a
    hash reference of attribute values.

    The default implementation accepts a hash or hash reference of named
    parameters. If it receives a single argument that isn't a hash reference
    it will throw 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.

        my ( $class, $options ) = @_;
        return $options->{foo};

    If you are inheriting from a non-Moo class, the arguments passed to the
    parent class constructor can be manipulated by defining a
    "FOREIGNBUILDARGS" method. It will receive the same arguments as
    "BUILDARGS", and should return a list of arguments to pass to the parent
    class constructor.

      sub BUILD {
        my ($self, $args) = @_;
        die "foo and bar cannot be used at the same time"
          if exists $args->{foo} && exists $args->{bar};

    On object creation, any "BUILD" methods in the class's inheritance
    hierarchy will be called on the object and given the results of
    "BUILDARGS". They each will be called in order from the parent classes
    down to the child, and thus should not themselves call the parent's
    method. Typically this is used for object validation or possibly

      sub DEMOLISH {
        my ($self, $in_global_destruction) = @_;

    When an object is destroyed, any "DEMOLISH" methods in the inheritance
    hierarchy will be called on the object. They are given boolean to inform
    them if global destruction is in progress, and are called from the child
    class upwards to the parent. This is similar to "BUILD" methods but in
    the opposite order.

    Note that this is implemented by a "DESTROY" method, which is only
    created on on the first construction of an object of your class. This
    saves on overhead for classes that are never instantiated or those
    without "DEMOLISH" methods. If you try to define your own "DESTROY",
    this will cause undefined results.

      extends 'Parent::Class';

    Declares a base class. Multiple superclasses can be passed for multiple
    inheritance but please consider using roles instead. The class will be
    loaded but no errors will be triggered if the class can't be found and
    there are already subs in the class.

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

      with 'Some::Role1';


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

    Composes one or more Moo::Role (or Role::Tiny) roles into the current
    class. An error will be raised if these roles cannot be composed because
    they have conflicting method definitions. The roles will be loaded using
    the same mechanism as "extends" uses.

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

    Declares an attribute for the class.

      package Foo;
      use Moo;
      has 'attr' => (
        is => 'ro'

      package Bar;
      use Moo;
      extends 'Foo';
      has '+attr' => (
        default => sub { "blah" },

    Using the "+" notation, it's possible to override an attribute.

      has [qw(attr1 attr2 attr3)] => (
        is => 'ro',

    Using an arrayref with multiple attribute names, it's possible to
    declare multiple attributes with the same options.

    The options for "has" are as follows:

      required, may be "ro", "lazy", "rwp" or "rw".

      "ro" stands for "read-only" and generates an accessor that dies if you
      attempt to write to it - i.e. a getter only - by defaulting "reader"
      to the name of the attribute.

      "lazy" generates a reader like "ro", but also sets "lazy" to 1 and
      "builder" to "_build_${attribute_name}" to allow on-demand generated
      attributes. This feature was my attempt to fix my incompetence when
      originally designing "lazy_build", and is also implemented by
      MooseX::AttributeShortcuts. There is, however, nothing to stop you
      using "lazy" and "builder" yourself with "rwp" or "rw" - it's just
      that this isn't generally a good idea so we don't provide a shortcut
      for it.

      "rwp" stands for "read-write protected" and generates a reader like
      "ro", but also sets "writer" to "_set_${attribute_name}" for
      attributes that are designed to be written from inside of the class,
      but read-only from outside. This feature comes from

      "rw" stands for "read-write" and generates a normal getter/setter by
      defaulting the "accessor" to the name of the attribute specified.

      Takes a coderef which is used to validate the attribute. Unlike Moose,
      Moo does not include a basic type system, so instead of doing "isa =>
      'Num'", one should do

        use Scalar::Util qw(looks_like_number);
        isa => sub {
          die "$_[0] is not a number!" unless looks_like_number $_[0]

      Note that the return value for "isa" is discarded. Only if the sub
      dies does type validation fail.

      Sub::Quote aware

      Since Moo does not run the "isa" check before "coerce" if a coercion
      subroutine has been supplied, "isa" checks are not structural to your
      code and can, if desired, be omitted on non-debug builds (although if
      this results in an uncaught bug causing your program to break, the Moo
      authors guarantee nothing except that you get to keep both halves).

      If you want Moose compatible or MooseX::Types style named types, look
      at Type::Tiny.

      To cause your "isa" entries to be automatically mapped to named
      Moose::Meta::TypeConstraint objects (rather than the default behaviour
      of creating an anonymous type), set:

        $Moo::HandleMoose::TYPE_MAP{$isa_coderef} = sub {
          require MooseX::Types::Something;
          return MooseX::Types::Something::TypeName();

      Note that this example is purely illustrative; anything that returns a
      Moose::Meta::TypeConstraint object or something similar enough to it
      to make Moose happy is fine.

      Takes a coderef which is meant to coerce the attribute. The basic idea
      is to do something like the following:

       coerce => sub {
         $_[0] % 2 ? $_[0] : $_[0] + 1

      Note that Moo will always execute your coercion: this is to permit
      "isa" entries to be used purely for bug trapping, whereas coercions
      are always structural to your code. We do, however, apply any supplied
      "isa" check after the coercion has run to ensure that it returned a
      valid value.

      Sub::Quote aware

      If the "isa" option is a blessed object providing a "coerce" or
      "coercion" method, then the "coerce" option may be set to just 1.

      Takes a string

        handles => 'RobotRole'

      Where "RobotRole" is a role that defines an interface which becomes
      the list of methods to handle.

      Takes a list of methods

        handles => [ qw( one two ) ]

      Takes a hashref

        handles => {
          un => 'one',

      Takes a coderef which will get called any time the attribute is set.
      This includes the constructor, but not default or built values. The
      coderef will be invoked against the object with the new value as an

      If you set this to just 1, it generates a trigger which calls the
      "_trigger_${attr_name}" method on $self. This feature comes from

      Note that Moose also passes the old value, if any; this feature is not
      yet supported.

      Sub::Quote aware

      Takes a coderef which will get called with $self as its only argument
      to populate an attribute if no value for that attribute was supplied
      to the constructor. Alternatively, if the attribute is lazy, "default"
      executes when the attribute is first retrieved if no value has yet
      been provided.

      If a simple scalar is provided, it will be inlined as a string. Any
      non-code reference (hash, array) will result in an error - for that
      case instead use a code reference that returns the desired value.

      Note that if your default is fired during new() there is no guarantee
      that other attributes have been populated yet so you should not rely
      on their existence.

      Sub::Quote aware

      Takes a method name which will return true if an attribute has a

      If you set this to just 1, the predicate is automatically named
      "has_${attr_name}" if your attribute's name does not start with an
      underscore, or "_has_${attr_name_without_the_underscore}" if it does.
      This feature comes from MooseX::AttributeShortcuts.

      Takes a method name which will be called to create the attribute -
      functions exactly like default except that instead of calling


      Moo will call


      The following features come from MooseX::AttributeShortcuts:

      If you set this to just 1, the builder is automatically named

      If you set this to a coderef or code-convertible object, that variable
      will be installed under "$class::_build_${attr_name}" and the builder
      set to the same name.

      Takes a method name which will clear the attribute.

      If you set this to just 1, the clearer is automatically named
      "clear_${attr_name}" if your attribute's name does not start with an
      underscore, or "_clear_${attr_name_without_the_underscore}" if it
      does. This feature comes from MooseX::AttributeShortcuts.

      NOTE: If the attribute is "lazy", it will be regenerated from
      "default" or "builder" the next time it is accessed. If it is not
      lazy, it will be "undef".

      Boolean. Set this if you want values for the attribute to be grabbed
      lazily. This is usually a good idea if you have a "builder" which
      requires another attribute to be set.

      Boolean. Set this if the attribute must be passed on object

      The name of the method that returns the value of the attribute. If you
      like Java style methods, you might set this to "get_foo"

      The value of this attribute will be the name of the method to set the
      value of the attribute. If you like Java style methods, you might set
      this to "set_foo".

      Boolean. Set this if you want the reference that the attribute
      contains to be weakened. Use this when circular references, which
      cause memory leaks, are possible.

      Takes the name of the key to look for at instantiation time of the
      object. A common use of this is to make an underscored attribute have
      a non-underscored initialization name. "undef" means that passing the
      value in on instantiation is ignored.

      Takes either a coderef or array of coderefs which is meant to
      transform the given attributes specifications if necessary when
      upgrading to a Moose role or class. You shouldn't need this by
      default, but is provided as a means of possible extensibility.

      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.

    To do this, you can write

      use Sub::Quote;

      use Moo;
      use namespace::clean;

      has foo => (
        is => 'ro',
        isa => quote_sub(q{ die "Not <3" unless $_[0] < 3 })

    which will be inlined as

      do {
        local @_ = ($_[0]->{foo});
        die "Not <3" unless $_[0] < 3;

    or to avoid localizing @_,

      has foo => (
        is => 'ro',
        isa => quote_sub(q{ my ($val) = @_; die "Not <3" unless $val < 3 })

    which will be inlined as

      do {
        my ($val) = ($_[0]->{foo});
        die "Not <3" unless $val < 3;

    See Sub::Quote for more information, including how to pass lexical
    captures that will also be compiled into the subroutine.

    Moo will not clean up imported subroutines for you; you will have to do
    that manually. The recommended way to do this is to declare your imports
    first, then "use Moo", then "use namespace::clean". Anything imported
    before namespace::clean will be scrubbed. Anything imported or declared
    after will be still be available.

      package Record;

      use Digest::MD5 qw(md5_hex);

      use Moo;
      use namespace::clean;

      has name => (is => 'ro', required => 1);
      has id => (is => 'lazy');
      sub _build_id {
        my ($self) = @_;
        return md5_hex($self->name);


    For example if you were to import these subroutines after
    namespace::clean like this

      use namespace::clean;

      use Digest::MD5 qw(md5_hex);
      use Moo;

    then any "Record" $r would have methods such as "$r->md5_hex()",
    "$r->has()" and "$r->around()" - almost certainly not what you intend!

    Moo::Roles behave slightly differently. Since their methods are composed
    into the consuming class, they can do a little more for you
    automatically. As long as you declare your imports before calling "use
    Moo::Role", those imports and the ones Moo::Role itself provides will
    not be composed into consuming classes so there's usually no need to use

    On namespace::autoclean: Older versions of namespace::autoclean would
    inflate Moo classes to full Moose classes, losing the benefits of Moo.
    If you want to use namespace::autoclean with a Moo class, make sure you
    are using version 0.16 or newer.

    There is no built-in type system. "isa" is verified with a coderef; if
    you need complex types, Type::Tiny can provide types, type libraries,
    and will work seamlessly with both Moo and Moose. Type::Tiny can be
    considered the successor to MooseX::Types and provides a similar API, so
    that you can write

      use Types::Standard qw(Int);
      has days_to_live => (is => 'ro', isa => Int);

    "initializer" is not supported in core since the author considers it to
    be a bad idea and Moose best practices recommend avoiding it. Meanwhile
    "trigger" or "coerce" are more likely to be able to fulfill your needs.

    No support for "super", "override", "inner", or "augment" - the author
    considers augment to be a bad idea, and override can be translated:

      override foo => sub {

      around foo => sub {
        my ($orig, $self) = (shift, shift);

    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 and plain scalars, because passing a
    hash or array reference as a default is almost always incorrect since
    the value is then shared between all objects using that default.

    "lazy_build" is not supported; you are instead encouraged to use the "is
    => 'lazy'" option supported by Moo and MooseX::AttributeShortcuts.

    "auto_deref" is not supported since the author considers it a bad idea
    and it has been considered best practice to avoid it for some time.

    "documentation" will show up in a Moose metaclass created from your
    class but is otherwise ignored. Then again, Moose ignores it as well, so
    this is arguably not an incompatibility.

    Since "coerce" does not require "isa" to be defined but Moose does
    require it, the metaclass inflation for coerce alone is a trifle insane
    and if you attempt to subtype the result will almost certainly break.

    Handling of warnings: when you "use Moo" we enable strict and warnings,
    in a similar way to Moose. The authors recommend the use of
    "strictures", which enables FATAL warnings, and several extra pragmas
    when used in development: indirect, multidimensional, and

    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

      package MyClass;
      use Moo;
      use strictures 2;

    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;

    There is no meta object. If you need this level of complexity you need
    Moose - Moo is small because it explicitly does not provide a
    metaprotocol. However, if you load Moose, then


    will return an appropriate metaclass pre-populated by Moo.

    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. ("make_immutable" is a no-op in Moo to ease migration.)

    An extension MooX::late exists to ease translating Moose packages to Moo
    by providing a more Moose-like interface.

    Moo is compatible with perl versions back to 5.6. When running on older
    versions, additional prerequisites will be required. If you are
    packaging a script with its dependencies, such as with App::FatPacker,
    you will need to be certain that the extra prerequisites are included.

        Required on perl versions prior to 5.10.0.

        Required on perl versions prior to 5.14.0.

    IRC: #moose on

    Bugtracker: <>

    Git repository: <git://>

    Git browser: <>

    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) <>

    Mithaldu - Christian Walde (cpan:MITHALDU)

    ilmari - Dagfinn Ilmari Mannsåker (cpan:ILMARI) <>

    tobyink - Toby Inkster (cpan:TOBYINK) <>

    haarg - Graham Knop (cpan:HAARG) <>

    mattp - Matt Phillips (cpan:MATTP) <>

    bluefeet - Aran Deltac (cpan:BLUEFEET) <>

    bubaflub - Bob Kuo (cpan:BUBAFLUB) <>

    ether = Karen Etheridge (cpan:ETHER) <>

    Copyright (c) 2010-2015 the Moo "AUTHOR" and "CONTRIBUTORS" as listed

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