Provided by: libmoo-perl_1.004002-1_all 
NAME
Moo - Minimalist Object Orientation (with Moose compatibility)
SYNOPSIS
package Cat::Food;
use Moo;
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 },
);
1;
And elsewhere:
my $full = Cat::Food->new(
taste => 'DELICIOUS.',
brand => 'SWEET-TREATZ',
pounds => 10,
);
$full->feed_lion;
say $full->pounds;
DESCRIPTION
This module is an extremely light-weight subset of Moose optimised for rapid startup and
"pay only for what you use".
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 compatibility with Moose's surface syntax,
preferring instead of 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 syntax, see
"INCOMPATIBILITIES WITH MOOSE".
WHY MOO EXISTS
If you want a full object system with a rich Metaprotocol, Moose is already wonderful.
However, sometimes you're writing a command line script or a CGI script where fast startup
is essential, or code designed to be deployed as a single file via App::FatPacker, or
you're writing a CPAN module and you want it to be usable by people with those
constraints.
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.
Better still, if you install and load Moose, we set up metaclasses for your Moo classes
and Moo::Role roles, so you can use them in Moose code without ever noticing that some of
your codebase is using Moo.
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
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 anybody
ever noticing you aren't using Moose everywhere.
Moo will also create Moose type constraints for classes and roles, so that "isa =>
'MyClass'" and "isa => 'MyRole'" work the same as for Moose classes and roles.
Extending a Moose class or consuming a Moose::Role will also work.
So will extending a Mouse class or consuming a Mouse::Role - 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 want types to be upgraded to the Moose types, use MooX::Types::MooseLike and
install the MooseX::Types library to match the MooX::Types::MooseLike library you're using
- Moo will load the MooseX::Types library and use that type for the newly created
metaclass.
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.
MOO AND CLASS::XSACCESSOR
If a new enough version of Class::XSAccessor is available, it will be used to generate
simple accessors, readers, and writers for a speed boost. Simple accessors are those
without lazy defaults, type checks/coercions, or triggers. Readers and writers generated
by Class::XSAccessor will behave slightly differently: they will reject attempts to call
them with the incorrect number of parameters.
MOO VERSUS ANY::MOOSE
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
<http://shadow.cat/blog/matt-s-trout/moo-versus-any-moose> which explains the differing
strategies in more detail and provides a direct example of where Moo succeeds and
Any::Moose fails.
IMPORTED METHODS
new
Foo::Bar->new( attr1 => 3 );
or
Foo::Bar->new({ attr1 => 3 });
BUILDARGS
sub BUILDARGS {
my ( $class, @args ) = @_;
unshift @args, "attr1" if @args % 2 == 1;
return { @args };
};
Foo::Bar->new( 3 );
The default implementation of this method accepts a hash or hash reference of named
parameters. If it receives a single argument that isn't a hash reference it throws an
error.
You can override this method in your class to handle other types of options passed to the
constructor.
This method should always return a hash reference of named options.
FOREIGNBUILDARGS
If you are inheriting from a non-Moo class, the arguments passed to the parent class
constructor can be manipulated by defining a "FOREIGNBUILDARGS" method. It will receive
the same arguments as "BUILDARGS", and should return a list of arguments to pass to the
parent class constructor.
BUILD
Define a "BUILD" method on your class and the constructor will automatically call the
"BUILD" method from parent down to child after the object has been instantiated.
Typically this is used for object validation or possibly logging.
DEMOLISH
If you have a "DEMOLISH" method anywhere in your inheritance hierarchy, a "DESTROY" method
is created on first object construction which will call
"$instance->DEMOLISH($in_global_destruction)" for each "DEMOLISH" method from child
upwards to parents.
Note that the "DESTROY" method is created on first construction of an object of your class
in order to not add overhead to classes without "DEMOLISH" methods; this may prove
slightly surprising if you try and define your own.
does
if ($foo->does('Some::Role1')) {
...
}
Returns true if the object composes in the passed role.
IMPORTED SUBROUTINES
extends
extends 'Parent::Class';
Declares base class. Multiple superclasses can be passed for multiple inheritance (but
please use roles instead). The class will be loaded, however no errors will be triggered
if it 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
with 'Some::Role1';
or
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 have conflicting methods. The roles will be loaded using
the same mechansim as "extends" uses.
has
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.
The options for "has" are as follows:
• is
required, may be "ro", "lazy", "rwp" or "rw".
"ro" 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_${attribute_name}" to allow on-demand generated attributes. This feature was my
attempt to fix my incompetence when originally designing "lazy_build", and is also
implemented by MooseX::AttributeShortcuts. There is, however, nothing to stop you using
"lazy" and "builder" yourself with "rwp" or "rw" - it's just that this isn't generally a
good idea so we don't provide a shortcut for it.
"rwp" generates a reader like "ro", but also sets "writer" to "_set_${attribute_name}"
for attributes that are designed to be written from inside of the class, but read-only
from outside. This feature comes from MooseX::AttributeShortcuts.
"rw" generates a normal getter/setter by defaulting "accessor" to the name of the
attribute.
• isa
Takes a coderef which is meant to validate the attribute. Unlike Moose, Moo does not
include a basic type system, so instead of doing "isa => 'Num'", one should do
isa => sub {
die "$_[0] is not a number!" unless looks_like_number $_[0]
},
Note that the return value is ignored, only whether the sub lives or dies matters.
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 MooseX::Types style named types, look at MooX::Types::MooseLike.
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.
• coerce
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] : $_[0] + 1
},
Note that Moo will always fire your coercion: this is to permit "isa" entries to be used
purely for bug trapping, whereas coercions are always structural to your code. We do,
however, apply any supplied "isa" check after the coercion has run to ensure that it
returned a valid value.
Sub::Quote aware
• handles
Takes a string
handles => 'RobotRole'
Where "RobotRole" is a role (Moo::Role) that defines an interface which becomes the list
of methods to handle.
Takes a list of methods
handles => [ qw( one two ) ]
Takes a hashref
handles => {
un => 'one',
}
• "trigger"
Takes a coderef which will get called any time the attribute is set. This includes the
constructor, but not default or built values. Coderef will be invoked against the object
with the new value as an argument.
If you set this to just 1, it generates a trigger which calls the
"_trigger_${attr_name}" method on $self. This feature comes from
MooseX::AttributeShortcuts.
Note that Moose also passes the old value, if any; this feature is not yet supported.
Sub::Quote aware
• "default"
Takes a coderef which will get called with $self as its only argument to populate an
attribute if no value is supplied to the constructor - or if the attribute is lazy, when
the attribute is first retrieved if no value has yet been provided.
If a simple scalar is provided, it will be inlined as a string. Any non-code reference
(hash, array) will result in an error - for that case instead use a code reference that
returns the desired value.
Note that if your default is fired during new() there is no guarantee that other
attributes have been populated yet so you should not rely on their existence.
Sub::Quote aware
• "predicate"
Takes a method name which will return true if an attribute has a value.
If you set this to just 1, the predicate is automatically named "has_${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.
• "builder"
Takes a method name which will be called to create the attribute - functions exactly
like default except that instead of calling
$default->($self);
Moo will call
$self->$builder;
The following features come from MooseX::AttributeShortcuts:
If you set this to just 1, the builder is automatically named "_build_${attr_name}".
If you set this to a coderef or code-convertible object, that variable will be installed
under "$class::_build_${attr_name}" and the builder set to the same name.
• "clearer"
Takes a method name which will clear the attribute.
If you set this to just 1, the clearer is automatically named "clear_${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.
• "lazy"
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.
• "required"
Boolean. Set this if the attribute must be passed on instantiation.
• "reader"
The value of this attribute will be the name of the method to get the value of the
attribute. If you like Java style methods, you might set this to "get_foo"
• "writer"
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".
• "weak_ref"
Boolean. Set this if you want the reference that the attribute contains to be weakened;
use this when circular references are possible, which will cause leaks.
• "init_arg"
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.
• "moosify"
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
before foo => sub { ... };
See "before method(s) => sub { ... }" in Class::Method::Modifiers for full documentation.
around
around foo => sub { ... };
See "around method(s) => sub { ... }" in Class::Method::Modifiers for full documentation.
after
after foo => sub { ... };
See "after method(s) => sub { ... }" in Class::Method::Modifiers for full documentation.
SUB QUOTE AWARE
"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 $val < 3;
}
See Sub::Quote for more information, including how to pass lexical captures that will also
be compiled into the subroutine.
CLEANING UP IMPORTS
Moo will not clean up imported subroutines for you; you will have to do that manually. The
recommended way to do this is to declare your imports first, then "use Moo", then "use
namespace::clean". Anything imported before namespace::clean will be scrubbed. Anything
imported or declared after will be still be available.
package Record;
use Digest::MD5 qw(md5_hex);
use Moo;
use namespace::clean;
has name => (is => 'ro', required => 1);
has id => (is => 'lazy');
sub _build_id {
my ($self) = @_;
return md5_hex($self->name);
}
1;
If you were to import "md5_hex" after namespace::clean you would be able to call
"->md5_hex()" on your "Record" instances (and it probably wouldn't do what you expect!).
Moo::Roles behave slightly differently. Since their methods are composed into the
consuming class, they can do a little more for you automatically. As long as you declare
your imports before calling "use Moo::Role", those imports and the ones Moo::Role itself
provides will not be composed into consuming classes, so there's usually no need to use
namespace::clean.
On namespace::autoclean: If you're coming to Moo from the Moose world, you may be
accustomed to using namespace::autoclean in all your packages. This is not recommended for
Moo packages, because namespace::autoclean will inflate your class to a full Moose class.
It'll work, but you will lose the benefits of Moo. Instead you are recommended to just
use namespace::clean.
INCOMPATIBILITIES WITH MOOSE
There is no built-in type system. "isa" is verified with a coderef; if you need complex
types, just make a library of coderefs, or better yet, functions that return quoted subs.
MooX::Types::MooseLike provides a similar API to MooseX::Types::Moose so that you can
write
has days_to_live => (is => 'ro', isa => Int);
and have it work with both; it is hoped that providing only subrefs as an API will
encourage the use of other type systems as well, since it's probably the weakest part of
Moose design-wise.
"initializer" is not supported in core since the author considers it to be a bad idea and
Moose best practices recommend avoiding it. Meanwhile "trigger" or "coerce" are more
likely to be able to fulfill your needs.
There is no meta object. If you need this level of complexity you wanted Moose - Moo
succeeds at being small because it explicitly does not provide a metaprotocol. However, if
you load Moose, then
Class::MOP::class_of($moo_class_or_role)
will return an appropriate metaclass pre-populated by Moo.
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 {
...
super();
...
};
around foo => sub {
my ($orig, $self) = (shift, shift);
...
$self->$orig(@_);
...
};
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.
"BUILDARGS" is not triggered if your class does not have any attributes. Without
attributes, "BUILDARGS" return value would be ignored, so we just skip calling the method
instead.
Handling of warnings: when you "use Moo" we enable FATAL warnings, and some several extra
pragmas when used in development: indirect, multidimensional, and bareword::filehandles.
See the strictures documentation for the details on this.
A 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
__PACKAGE__->meta->make_immutable;
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.
SUPPORT
Users' IRC: #moose on irc.perl.org
Development and contribution IRC: #web-simple on irc.perl.org
Bugtracker: <https://rt.cpan.org/Public/Dist/Display.html?Name=Moo>
Git repository: <git://github.com/moose/Moo.git>
Git browser: <https://github.com/moose/Moo>
AUTHOR
mst - Matt S. Trout (cpan:MSTROUT) <mst@shadowcat.co.uk>
CONTRIBUTORS
dg - David Leadbeater (cpan:DGL) <dgl@dgl.cx>
frew - Arthur Axel "fREW" Schmidt (cpan:FREW) <frioux@gmail.com>
hobbs - Andrew Rodland (cpan:ARODLAND) <arodland@cpan.org>
jnap - John Napiorkowski (cpan:JJNAPIORK) <jjn1056@yahoo.com>
ribasushi - Peter Rabbitson (cpan:RIBASUSHI) <ribasushi@cpan.org>
chip - Chip Salzenberg (cpan:CHIPS) <chip@pobox.com>
ajgb - Alex J. G. BurzyXski (cpan:AJGB) <ajgb@cpan.org>
doy - Jesse Luehrs (cpan:DOY) <doy at tozt dot net>
perigrin - Chris Prather (cpan:PERIGRIN) <chris@prather.org>
Mithaldu - Christian Walde (cpan:MITHALDU) <walde.christian@googlemail.com>
ilmari - Dagfinn Ilmari Mannsaaker (cpan:ILMARI) <ilmari@ilmari.org>
tobyink - Toby Inkster (cpan:TOBYINK) <tobyink@cpan.org>
haarg - Graham Knop (cpan:HAARG) <haarg@cpan.org>
mattp - Matt Phillips (cpan:MATTP) <mattp@cpan.org>
bluefeet - Aran Deltac (cpan:BLUEFEET) <bluefeet@gmail.com>
COPYRIGHT
Copyright (c) 2010-2011 the Moo "AUTHOR" and "CONTRIBUTORS" as listed above.
LICENSE
This library is free software and may be distributed under the same terms as perl itself.
See <http://dev.perl.org/licenses/>.