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Manual Reference Pages  -  MOOSEX::ATTRIBUTESHORTCUTS (3)

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MooseX::AttributeShortcuts - Shorthand for common attribute options



This document describes version 0.017 of MooseX::AttributeShortcuts - released October 28, 2012 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 youd 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

<B>NOTE:B> 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! }); effectively the same as...

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

    constraint => sub { ... }

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


    # 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.


The development version is on github at <> and may be cloned from <git://>


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 <>


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

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