Moops - Moops Object-Oriented Programming Sugar


   use Moops;
   role NamedThing {
      has name => (is => "ro", isa => Str);
   class Person with NamedThing;
   class Company with NamedThing;
   class Employee extends Person {
      has job_title => (is => "rwp", isa => Str);
      has employer  => (is => "rwp", isa => InstanceOf["Company"]);
      method change_job ( Object $employer, Str $title ) {
      method promote ( Str $title ) {



Until version 1.000, stuff might change, but not without good reason.


Moops is sugar for declaring and using roles and classes in Perl.

The syntax is inspired by MooseX::Declare, and Stevan Little's p5-mop-redux project (which is in turn partly inspired by Perl 6).

Moops has fewer than half of the dependencies as MooseX::Declare, loads in about 25% of the time, and the classes built with it run significantly faster. Moops does not use Devel::Declare, instead using Perl's pluggable keyword API; this requires Perl 5.14 or above.

Moops uses Moo to build classes and roles by default, but allows you to use Moose if you desire. (And Mouse experimentally.)


The class keyword declares a class:

   class Foo {
      # ...

A version number can be provided:

   class Foo 1.2 {
      # ...

If no version is provided, your class' $VERSION variable is set to the empty string; this helps the package be seen by Class::Load.

If your class extends an existing class through inheritance, or consumes one or more roles, these can also be provided when declaring the class.

   class Foo::Bar 1.2 extends Foo with Magic::Monkeys {
      # ...

If you use Moops within a package other than main, then package names used within the declaration are "qualified" by that outer package, unless they contain "::". So for example:

   package Quux;
   use Moops;
   class Foo { }       # declares Quux::Foo
   class Xyzzy::Foo    # declares Xyzzy::Foo
      extends Foo { }  # ... extending Quux::Foo
   class ::Baz { }     # declares Baz

If you wish to use Moose or Mouse instead of Moo; include that in the declaration:

   class Foo using Moose {
      # ...

It's also possible to create classes using Tiny (Class::Tiny), but there's probably little point in it, because Moops uses Moo internally, so the more capable Moo is already loaded and in memory.

(The using option is exempt from the package qualification rules mentioned earlier.)

Moops uses MooseX::MungeHas in your classes so that the has keyword supports some Moo-specific features, even when you're using Moose or Mouse. Specifically, it supports is => 'rwp', is => 'lazy', builder => 1, clearer => 1, predicate => 1, and trigger => 1. If you're using Moo, the MooX::late extension is enabled too, which allows Moose-isms in Moo too. With the combination of these features, there should be very little difference between Moo, Mouse and Moose has keywords.

Moose classes are automatically accelerated using MooseX::XSAccessor if it's installed.

Note that it is possible to declare a class with an empty body; use a trailing semicolon.

   class Employee extends Person with Employment;

If using Moose or Mouse, classes are automatically made immutable.

namespace::sweep is automatically used in all classes.

Between the class declaration and its body, Attribute::Handlers-style attributes may be provided:

   class Person :mutable {
      # ...
   class Employee extends Person with Employment :mutable;

The following attributes are defined for classes:

  • :assertions - enables assertion checking (see below)

  • :dirty - suppresses namespace::sweep

  • :mutable - suppresses making Moose classes immutable

  • :ro - make attributes declared with has default to 'ro'

  • :rw - make attributes declared with has default to 'rw'

  • :rwp - make attributes declared with has default to 'rwp'


Roles can be declared similarly to classes, but using the role keyword.

   role Stringable
      using Moose     # we know you meant Moose::Role
      # ...

Roles do not support the extends option.

Roles can be declared to be using Moo, Moose, Mouse or Tiny. (Note that if you're mixing and matching role frameworks, there are limitations to which class builders can consume which roles. Mouse is generally the least compatible; Moo and Moose classes should be able to consume each others' roles; Moo can also consume Role::Tiny roles.)

If roles use Moo, the MooX::late extension is enabled.

namespace::sweep is automatically used in all roles.

Roles take similar Attribute::Handlers-style attributes to classes, but don't support :mutable.


The namespace keyword works as above, but declares a package without any class-specific or role-specific semantics.

   namespace Utils {
      # ...

namespace::sweep is not automatically used in namespaces.

Attribute::Handlers-style attributes are supported for namespaces, but most of the built-in attributes make any sense without class/role semantics. (:assertions does.) Traits written as Moops extensions may support namespaces.

Functions and Methods

Moops uses Function::Parameters to declare functions and methods within classes and roles, which is perhaps not as featureful as Method::Signatures, but it does the job.

   class Person {
      use Scalar::Util 'refaddr';
      has name => (is => 'rwp');    # Moo attribute
      method change_name ( Str $newname ) {
         $self->_set_name( $newname )
            unless $newname eq 'Princess Consuela Banana-Hammock';
      fun is_same_as ( Object $x, Object $y ) {
         refaddr($x) == refaddr($y)
   my $phoebe = Person->new(name => 'Phoebe');
   my $ursula = Person->new(name => 'Ursula');
   Person::is_same_as($phoebe, $ursula);   # false

Note function signatures use type constraints from Types::Standard; MooseX::Types and MouseX::Types type constraints should also work, provided you use their full names, including their package.

The is_same_as function above could have been written as a class method like this:

   class Person {
      # ...
      method is_same_as ( $class: Object $x, Object $y ) {
         refaddr($x) == refaddr($y)
   # ...
   Person->is_same_as($phoebe, $ursula);   # false

The method keyword is not provided within packages declared using namespace; it is only available within classes and roles.

Within Moose classes and roles, the MooseX::FunctionParametersInfo module is loaded, to allow access to method signatures via the meta object protocol. (This is currently broken for around method modifiers.)

Method Modifiers

Within classes and roles, before, after and around keywords are provided for declaring method modifiers. These use the same syntax as method.

Unlike Moo/Mouse/Moose, for around modifiers, the coderef being wrapped is not passed as $_[0]. Instead, it's available in the global variable ${^NEXT}.

Type Constraints

The Types::Standard type constraints are exported to each package declared using Moops. This allows the standard type constraints to be used as barewords.

If using type constraints from other type constraint libraries, they should generally be usable by package-qualifying them:

   use MooseX::Types::Numeric qw();
   method foo ( MooseX::Types::Common::Numeric::PositiveInt $d ) {
      # ...


   use MooseX::Types::Common::Numeric qw(PositiveInt);
   method foo ( (SingleDigit) $d ) {
      # ...

Note the parentheses around the type constraint in the method signature; this is required for Function::Parameters to realise that SingleDigit is an imported symbol, and not a string to be looked up.

(The version using the fully-qualified name should even work in Moo and Mouse classes, because it forces the type constraint to be loaded via (and wrapped by) Type::Tiny.)


The useful constants true and false are imported into all declared packages. (Within classes and roles, namespace::sweep will later remove them from the symbol table, so they don't form part of your package's API.) These constants can help make attribute declarations more readable.

   has name => (is => 'ro', isa => Str, required => true);

Further constants can be declared using the define keyword (see PerlX::Define):

   namespace Maths {
      define PI = 3.2;

Constants declared this way will not be swept away by namespace::sweep, and are considered part of your package's API.


Declared packages can contain assertions (see PerlX::Assert). These are normally optimized away at compile time, but you can force them to be checked using the :assertions attribute.

   class Foo {
      assert(false);    # not checked; optimized away
   class Bar :assertions {
      assert(false);    # checked; fails; throws exception

More Sugar

Strictures, including fatal warnings, but excluding the uninitialized, void, once and numeric warning categories is imported into all declared packages.

Perl 5.14 features, including the state and say keywords, and sane Unicode string handling are imported into all declared packages.

Try::Tiny is imported into all declared packages.

Scalar::Util's blessed and Carp's confess are imported into all declared packages.

Outer Sugar

The "outer" package, where the use Moops statement appears also gets a little sugar: strictures, the same warnings as "inner" packages, and Perl 5.14 features are all switched on.

true is loaded, so you don't need to do this at the end of your file:


Custom Sugar

It is possible to inject other functions into all inner packages using:

   use Moops [
      'List::Util'      => [qw( first reduce )],
      'List::MoreUtils' => [qw( any all none )],

This is by far the easiest way to extend Moops with project-specific extras.


Moops is written to hopefully be fairly extensible.

Extending Moops via imports

The easiest way to extend Moops is to inject additional imports into the inner packages using the technique outlined in "Custom Sugar" above. You can wrap all that up in a module:

   package MoopsX::Lists;
   use Moops ();
   use List::Util ();
   use List::MoreUtils ();
   sub import {
      push @{ $_[1] ||= [] }, (
         'List::Util'      => [qw( first reduce )],
         'List::MoreUtils' => [qw( any all none )],
      goto \&Moops::import;

Now people can do use MoopsX::Lists instead of use Moops.

Extending Moops via subclassing

For more complex needs, you should create a subclass of Moops, and override the class_for_parser method to inject your own custom keyword parser, which should be a subclass of Moops::Parser.

The parser subclass might want to override:

  • The keywords class method, which returns the list of keywords the parser can handle.

  • The class_for_keyword object method, which returns the name of a subclass of Moops::Keyword which will be used for translating the result of parsing the keyword into a string using Perl's built-in syntax.

Hopefully you'll be able to avoid overriding the parse method itself, as it has a slightly messy API.

Your class_for_keyword subclass can either be a direct subclass of Moops::Keyword, or of Moops::Keyword::Class or Moops::Keyword::Role.

The keyword subclass might want to override:

  • The known_relationships class method, which returns a list of valid inter-package relationships such as extends and using for the current keyword.

  • The qualify_relationship object method, which, when given the name of an inter-package relationship, indicates whether it should be subjected to package qualification rules (like extends and with are, but using is not).

  • The generate_package_setup object method which returns a list of strings to inject into the package.

  • The arguments_for_function_parameters object method which is used by the default generate_package_setup method to set up the arguments to be passed to Function::Parameters.

Hopefully you'll be able to avoid overriding the generate_code method.

Extending Moops via traits

Roles in the Moops::TraitFor::Keyword namespace are automatically loaded and applied to keyword objects when a corresponding Attribute::Handlers-style attribute is seen.

For examples extending Moops this way, see the Moops::TraitFor::Keyword::dirty, Moops::TraitFor::Keyword::mutable, Moops::TraitFor::Keyword::ro, Moops::TraitFor::Keyword::rw and Moops::TraitFor::Keyword::rwp traits.


Please report any bugs to


Similar: MooseX::Declare,

Main functionality exposed by this module: Moo/MooX::late, Function::Parameters, Try::Tiny, Types::Standard, namespace::sweep, true.

Internals fueled by: Keyword::Simple, Module::Runtime, Import::Into, Devel::Pragma, Attribute::Handlers.


Toby Inkster <>.


This software is copyright (c) 2013 by Toby Inkster.

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.