++ed by:

10 PAUSE users
4 non-PAUSE users.

Chris Weyl


MooseX::AttributeShortcuts - Shorthand for common attribute options


This document describes version 0.022 of MooseX::AttributeShortcuts - released September 29, 2013 as part of MooseX-AttributeShortcuts.


    package Some::Class;

    use Moose;
    use MooseX::AttributeShortcuts;

    # same as:
    #   is => 'ro', lazy => 1, builder => '_build_foo'
    has foo => (is => 'lazy');

    # same as: is => 'ro', writer => '_set_foo'
    has foo => (is => 'rwp');

    # same as: is => 'ro', builder => '_build_bar'
    has bar => (is => 'ro', builder => 1);

    # same as: is => 'ro', clearer => 'clear_bar'
    has bar => (is => 'ro', clearer => 1);

    # same as: is => 'ro', predicate => 'has_bar'
    has bar => (is => 'ro', predicate => 1);

    # works as you'd expect for "private": predicate => '_has_bar'
    has _bar => (is => 'ro', predicate => 1);

    # extending? Use the "Shortcuts" trait alias
    extends 'Some::OtherClass';
    has '+bar' => (traits => [Shortcuts], builder => 1, ...);

    # or...
    package Some::Other::Class;

    use Moose;
    use MooseX::AttributeShortcuts -writer_prefix => '_';

    # same as: is => 'ro', writer => '_foo'
    has foo => (is => 'rwp');


Ever find yourself repeatedly specifying writers and builders, because there's no good shortcut to specifying them? Sometimes you want an attribute to have a read-only public interface, but a private writer. And wouldn't it be easier to just say "builder => 1" and have the attribute construct the canonical "_build_$name" builder name for you?

This package causes an attribute trait to be applied to all attributes defined to the using class. This trait extends the attribute option processing to handle the above variations.


This package automatically applies an attribute metaclass trait. Unless you want to change the defaults, you can ignore the talk about "prefixes" below.


If you're extending a class and trying to extend its attributes as well, you'll find out that the trait is only applied to attributes defined locally in the class. This package exports a trait shortcut function "Shortcuts" that will help you apply this to the extended attribute:

    has '+something' => (traits => [Shortcuts], ...);


We accept two parameters on the use of this module; they impact how builders and writers are named.


    use MooseX::::AttributeShortcuts -writer_prefix => 'prefix';

The default writer prefix is '_set_'. If you'd prefer it to be something else (say, '_'), this is where you'd do that.


    use MooseX::::AttributeShortcuts -builder_prefix => 'prefix';

The default builder prefix is '_build_', as this is what lazy_build does, and what people in general recognize as build methods.


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

Want to see additional options? Ask, or better yet, fork on GitHub and send a pull request. If the shortcuts you're asking for already exist in Moo or Mouse or elsewhere, please note that as it will carry significant weight.

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

is => 'rwp'

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

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

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"

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")

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).

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,

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

...is effectively the same as...

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

isa => ..., constraint => sub { ... }

Specifying the constraint option with a coderef will cause a new subtype constraint to be created, with the parent type being the type specified in the isa option and the constraint being the coderef supplied here.

For example, only integers greater than 10 will pass this attribute's type constraint:

    # value must be an integer greater than 10 to pass the constraint
    has thinger => (
        isa        => 'Int',
        constraint => sub { $_ > 10 },
        # ...

Note that if you supply a constraint, you must also provide an isa.

isa => ..., constraint => sub { ... }, coerce => 1

Supplying a constraint and asking for coercion will "Just Work", that is, any coercions that the isa type has will still work.

For example, let's say that you're using the File type constraint from MooseX::Types::Path::Class, and you want an additional constraint that the file must exist:

    has thinger => (
        is         => 'ro',
        isa        => File,
        constraint => sub { !! $_->stat },
        coerce     => 1,

thinger will correctly coerce the string "/etc/passwd" to a Path::Class:File, and will only accept the coerced result as a value if the file exists.

coerce => [ Type => sub { ...coerce... }, ... ]

Specifying the coerce option with a hashref will cause a new subtype to be created and used (just as with the constraint option, above), with the specified coercions added to the list. In the passed hashref, the keys are Moose types (well, strings resolvable to Moose types), and the values are coderefs that will coerce a given type to our type.

    has bar => (
        is     => 'ro',
        isa    => 'Str',
        coerce => [
            Int    => sub { "$_"                       },
            Object => sub { 'An instance of ' . ref $_ },


Note that we create new, anonymous subtypes whenever the constraint or coercion options are specified in such a way that the Shortcuts trait (this one) is invoked. It's fully supported to use both constraint and coerce options at the same time.

This facility is intended to assist with the creation of one-off type constraints and coercions. It is not possible to deliberately reuse the subtypes we create, and if you find yourself using a particular isa / constraint / coerce option triplet in more than one place you should really think about creating a type that you can reuse. MooseX::Types provides the facilities to easily do this, or even a simple constant definition at the package level with an anonymous type stashed away for local use.


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


The development version is on github at http://github.com/RsrchBoy/moosex-attributeshortcuts and may be cloned from git://github.com/RsrchBoy/moosex-attributeshortcuts.git


Please report any bugs or feature requests on the bugtracker website https://github.com/RsrchBoy/moosex-attributeshortcuts/issues

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 <cweyl@alumni.drew.edu>


This software is Copyright (c) 2011 by Chris Weyl.

This is free software, licensed under:

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