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Reindeer - Moose with more antlers


This document describes version 0.020 of Reindeer - released December 20, 2017 as part of Reindeer.


    # ta-da!
    use Reindeer;

    # the same as:
    use feature ':5.xx'; # where xx is appropriate for your running perl
    use Moose;
    use MooseX::MarkAsMethods autoclean => 1;
    use MooseX::AlwaysCoerce;
    use MooseX::AttributeShortcuts;
    # etc, etc, etc


Like Moose? Use MooseX::* extensions? Maybe some MooseX::Types libraries? Hate that you have to use them in every. Single. Class.

Reindeer aims to resolve that :) Reindeer _is_ Moose -- it's just Moose with a number of the more useful/popular extensions already applied. Reindeer is a drop-in replacement for your "use Moose" line, that behaves in the exact same way... Just with more pointy antlers.


Be aware this package should be considered early release code. While Moose and all our incorporated extensions have their own classifications (generally GA or "stable"), this bundling is still under active development, and more extensions, features and the like may still be added.

That said, my goal here is to increase functionality, not decrease it.

When this package hits GA / stable, I'll set the release to be >= 1.000.



This method allows you to easily compose a new class with additional traits:

    my $foo = Bar->with_traits('Stools', 'Norm')->new(beer => 1, tab => undef);

(See also MooseX::Traits.)


Unless specified here, all options defined by Moose::Meta::Attribute and Class::MOP::Attribute remain unchanged.

For the following, "$name" should be read as the attribute name; and the various prefixes should be read using the defaults

coerce => 0

Coercion is ENABLED by default; explicitly pass "coerce => 0" to disable.

(See also MooseX::AlwaysCoerce.)

lazy_require => 1

The reader methods for all attributes with that option will throw an exception unless a value for the attributes was provided earlier by a constructor parameter or through a writer method.

(See also MooseX::LazyRequire.)

is => 'rwp'

Specifying is => 'rwp' will cause the following options to be set:

    is     => 'ro'
    writer => "_set_$name"

rwp can be read as "read + write private".

is => 'lazy'

Specifying is => 'lazy' will cause the following options to be set:

    is       => 'ro'
    builder  => "_build_$name"
    lazy     => 1

NOTE: Since 0.009 we no longer set init_arg => undef if no init_arg is explicitly provided. This is a change made in parallel with Moo, based on a large number of people surprised that lazy also made one's init_def undefined.

is => 'lazy', default => ...

Specifying is => 'lazy' and a default will cause the following options to be set:

    is       => 'ro'
    lazy     => 1
    default  => ... # as provided

That is, if you specify is => 'lazy' and also provide a default, then we won't try to set a builder, as well.

builder => 1

Specifying builder => 1 will cause the following options to be set:

    builder => "_build_$name"

builder => sub { ... }

Passing a coderef to builder will cause that coderef to be installed in the class this attribute is associated with the name you'd expect, and builder => 1 to be set.

e.g., in your class (or role),

    has foo => (is => 'ro', builder => sub { 'bar!' }); effectively the same as...

    has foo => (is => 'ro', builder => '_build_foo');
    sub _build_foo { 'bar!' }

The behaviour of this option in roles changed in 0.030, and the builder methods will be installed in the role itself. This means you can alias/exclude/etc builder methods in roles, just as you can with any other method.

clearer => 1

Specifying clearer => 1 will cause the following options to be set:

    clearer => "clear_$name"

or, if your attribute name begins with an underscore:

    clearer => "_clear$name"

(that is, an attribute named _foo would get _clear_foo)

predicate => 1

Specifying predicate => 1 will cause the following options to be set:

    predicate => "has_$name"

or, if your attribute name begins with an underscore:

    predicate => "_has$name"

(that is, an attribute named _foo would get _has_foo)

init_arg => 1 / -1

This is a somewhat esoteric shortcut; you probably don't want to use this (or even read this section).

Specifying init_arg => 1 will cause the following options to be set:

    # attribute: "name"
    init_arg => 'name'

    # or, attribute: "_name"
    init_arg => '_name'

...while init_arg => -1 will cause the following options to be set:

    # attribute: "name"
    init_arg => '_name'

    # or, attribute: "_name"
    init_arg => 'name'

trigger => 1

Specifying trigger => 1 will cause the attribute to be created with a trigger that calls a named method in the class with the options passed to the trigger. By default, the method name the trigger calls is the name of the attribute prefixed with _trigger_.

e.g., for an attribute named foo this would be equivalent to:

    trigger => sub { shift->_trigger_foo(@_) }

For an attribute named _foo:

    trigger => sub { shift->_trigger__foo(@_) }

This naming scheme, in which the trigger is always private, is the same as the builder naming scheme (just with a different prefix).

handles => { foo => sub { ... }, ... }

Creating a delegation with a coderef will now create a new, "custom accessor" for the attribute. These coderefs will be installed and called as methods on the associated class (just as readers, writers, and other accessors are), and will have the attribute metaclass available in $_. Anything the accessor is called with it will have access to in @_, just as you'd expect of a method.

e.g., the following example creates an attribute named bar with a standard reader accessor named bar and two custom accessors named foo and foo_too.

    has bar => (

        is      => 'ro',
        isa     => 'Int',
        handles => {

            foo => sub {
                my $self = shift @_;

                return $_->get_value($self) + 1;

            foo_too => sub {
                my $self = shift @_;

                return $self->bar + 1;

            # you'd expect.
            bar => 'bar',

...and later,

Note that in this example both foo() and foo_too() do effectively the same thing: return the attribute's current value plus 1. However, foo() accesses the attribute value directly through the metaclass, the pros and cons of which this author leaves as an exercise for the reader to determine.

You may choose to use the installed accessors to get at the attribute's value, or use the direct metaclass access, your choice.


In addition to all sugar provided by Moose (e.g. has, with, extends), we provide a couple new keywords.

class_type ($class, ?$options)

Creates a new subtype of Object with the name $class and the metaclass Moose::Meta::TypeConstraint::Class.

  # Create a type called 'Box' which tests for objects which ->isa('Box')
  class_type 'Box';

By default, the name of the type and the name of the class are the same, but you can specify both separately.

  # Create a type called 'Box' which tests for objects which ->isa('ObjectLibrary::Box');
  class_type 'Box', { class => 'ObjectLibrary::Box' };

(See also Moose::Util::TypeConstraints.)

role_type ($role, ?$options)

Creates a Role type constraint with the name $role and the metaclass Moose::Meta::TypeConstraint::Role.

  # Create a type called 'Walks' which tests for objects which ->does('Walks')
  role_type 'Walks';

By default, the name of the type and the name of the role are the same, but you can specify both separately.

  # Create a type called 'Walks' which tests for objects which ->does('MooseX::Role::Walks');
  role_type 'Walks', { role => 'MooseX::Role::Walks' };

(See also Moose::Util::TypeConstraints.)

class_has => (...)

Exactly like "has" in Moose, but operates at the class (rather than instance) level.

(See also MooseX::ClassAttribute.)


default_for() is a shortcut to extend an attribute to give it a new default; this default value may be any legal value for default options.

    # attribute bar defined elsewhere (e.g. superclass)
    default_for bar => 'new default';

... is the same as:

    has '+bar' => (default => 'new default');


abstract() allows one to declare a method dependency that must be satisfied by a subclass before it is invoked, and before the subclass is made immutable.

    abstract 'method_name_that_must_be_satisfied';


requires() is a synonym for abstract() and works in the way you'd expect.


It is safe to use overloads in your Reindeer classes and roles; they will work just as you expect: overloads in classes can be inherited by subclasses; overloads in roles will be incorporated into consuming classes.

(See also MooseX::MarkAsMethods)


We export the following trait aliases. These traits are not automatically applied to attributes, and are lazily loaded (e.g. if you don't use them, they won't be loaded and are not dependencies).

They can be used by specifying them as:

    has foo => (traits => [ TraitAlias ], ...);


    has foo => (
        traits  => [ AutoDestruct ],
        is      => 'ro',
        lazy    => 1,
        builder => 1,
        ttl     => 600,

Allows for a "ttl" attribute option; this is the length of time (in seconds) that a stored value is allowed to live; after that time the value is cleared and the value rebuilt (given that the attribute is lazy and has a builder defined).

See MooseX::AutoDestruct for more information.


This attribute trait allows one to designate that certain attributes are to be cleared when certain other ones are; that is, when an attribute is cleared that clearing will be cascaded down to other attributes. This is most useful when you have attributes that are lazily built.

See MooseX::CascadeClearing for more information and a significantly more cogent description.


This is a Moose attribute trait that you use when you want the default value for an attribute to be populated from the %ENV hash. So, for example if you have set the environment variable USERNAME to 'John' you can do:

    package MyApp::MyClass;
    use Reindeer;

    has 'username' => (is=>'ro', traits=>[ ENV ]);

    package main;

    my $myclass = MyApp::MyClass->new();

    print $myclass->username; # STDOUT => 'John';

This is basically similar functionality to something like:

    has 'attr' => (
            default=> sub {
                    $ENV{uc 'attr'};

If the named key isn't found in %ENV, then defaults will execute as normal.

See MooseX::Attribute::ENV for more information.


    has 'data' => (
        traits    => [ MultiInitArg ],
        is        => 'ro',
        isa       => 'Str',
        init_args => [qw(munge frobnicate)],

This trait allows your attribute to be initialized with any one of multiple arguments to new().

See MooseX::MultiInitArg for more information.


Applying this trait to your attribute makes it's initialization tolerant of of undef. If you specify the value of undef to any of the attributes they will not be initialized (or will be set to the default, if applicable). Effectively behaving as if you had not provided a value at all.

    package My::Class;
    use Reindeer;

    has 'bar' => (
        traits    => [ UndefTolerant ],
        is        => 'ro',
        isa       => 'Num',
        predicate => 'has_bar'

    # Meanwhile, under the city...

    # Doesn't explode
    my $class = My::Class->new(bar => undef);
    $class->has_bar # False!

See MooseX::UndefTolerant::Attribute for more information.


Reindeer includes the traits and sugar provided by the following extensions. Everything their docs say they can do, you can do by default with Reindeer.








Note that this causes any overloads you've defined in your class/role to be marked as methods, and namespace::autoclean invoked.




This provides a new class method, with_traits(), allowing you to compose traits in on the fly:

    my $foo = Bar->with_traits('Stools')->new(...);









Non-Moose specific items made available to your class/role:

Perl v5.10+ features

If you're running on v5.10 or greater of Perl, Reindeer will automatically enable the default feature set of that level of Perl in the consuming class. (e.g. if you're running Perl v5.26, this is the same as use v5.26 or use feature ':5.26')


Technically, this is done by MooseX::MarkAsMethods, but it's worth pointing out here. Any overloads present in your class/role are marked as methods before autoclean is unleashed, so Everything Will Just Work as Expected.


  use Path::Class;
  my $dir  = dir('foo', 'bar');       # Path::Class::Dir object
  my $file = file('bob', 'file.txt'); # Path::Class::File object
  # Stringifies to 'foo/bar' on Unix, 'foo\bar' on Windows, etc.
  print "dir: $dir\n";
  # Stringifies to 'bob/file.txt' on Unix, 'bob\file.txt' on Windows
  print "file: $file\n";
  my $subdir  = $dir->subdir('baz');  # foo/bar/baz
  my $parent  = $subdir->parent;      # foo/bar
  my $parent2 = $parent->parent;      # foo
  my $dir2 = $file->dir;              # bob

  # Work with foreign paths
  use Path::Class qw(foreign_file foreign_dir);
  my $file = foreign_file('Mac', ':foo:file.txt');
  print $file->dir;                   # :foo:
  print $file->as_foreign('Win32');   # foo\file.txt
  # Interact with the underlying filesystem:
  # $dir_handle is an IO::Dir object
  my $dir_handle = $dir->open or die "Can't read $dir: $!";
  # $file_handle is an IO::File object
  my $file_handle = $file->open($mode) or die "Can't read $file: $!";

See the Path::Class documentation for more detail.


You can use Try::Tiny's try and catch to expect and handle exceptional conditions, avoiding quirks in Perl and common mistakes:

  # handle errors with a catch handler
  try {
    die "foo";
  } catch {
    warn "caught error: $_"; # not $@

You can also use it like a standalone eval to catch and ignore any error conditions. Obviously, this is an extreme measure not to be undertaken lightly:

  # just silence errors
  try {
    die "foo";

See the Try::Tiny documentation for more detail.


This author is applying his own assessment of "useful/popular extensions". You may find yourself in agreement, or violent disagreement with his choices. YMMV :)


Reindeer serves largely to tie together other packages -- Moose extensions and other common modules. Those other packages are largely by other people, without whose work Reindeer would have a significantly smaller rack.

We also use documentation as written for the other packages pulled in here to help present a cohesive whole.


Please see those modules/websites for more information related to this module.


Please report any bugs or feature requests on the bugtracker website

When submitting a bug or request, please include a test-file or a patch to an existing test-file that illustrates the bug or desired feature.


Chris Weyl <>


  • Alex Balhatchet <>

  • Mark Fowler <>


This software is Copyright (c) 2017, 2015, 2014, 2012, 2011 by Chris Weyl.

This is free software, licensed under:

  The GNU Lesser General Public License, Version 2.1, February 1999

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Around line 656:

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