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MooX-Const-v0.7.2
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NAME

MooX::Const - Syntactic sugar for constant and write-once Moo(se) attributes

SYNOPSIS

use Moo;
use MooX::Const;

use Types::Standard -types;

has thing => (
  is  => 'const',
  isa => ArrayRef[HashRef],
);

DESCRIPTION

This is syntactic sugar for using Types::Const with Moo. The SYNOPSIS above is equivalent to:

use Types::Const -types;

has thing => (
  is     => 'ro',
  isa    => Const[ArrayRef[HashRef]],
  coerce => 1,
);

It modifies the has function to support "const" attributes. These are read-only ("ro") attributes for references, where the underlying data structure has been set as read-only.

This will return an error if there is no "isa", the "isa" is not a code reference (v0.7.0) or a Type::Tiny type that is is not a reference, or a blessed object.

Simple value types such as Int or Str are silently converted to read-only attributes.

As of v0.5.0, it also supports write-once ("once") attributes for references:

has setting => (
  is  => 'once',
  isa => HashRef,
);

This allows you to set the attribute once. The value is coerced into a constant, and cannot be changed again.

Note that "wo" is a removed synonym for "once". It no longer works in v0.6.0, since "wo" is used for "write-only" in some Moose-like extensions.

As of v0.4.0, this now supports the strict setting:

has thing => (
  is     => 'const',
  isa    => ArrayRef[HashRef],
  strict => 0,
);

When this is set to a false value, then the read-only constraint will only be applied when running in strict mode, see Devel::StrictMode.

If omitted, strict is assumed to be true.

RECENT CHANGES

Changes for version v0.7.2 (2026-02-24)

See the Changes file for more details.

REQUIREMENTS

This module lists the following modules as runtime dependencies:

See the cpanfile file for the full list of prerequisites.

INSTALLATION

The latest version of this module (along with any dependencies) can be installed from CPAN with the cpan tool that is included with Perl:

cpan MooX::Const

You can also extract the distribution archive and install this module (along with any dependencies):

cpan .

You can also install this module manually using the following commands:

perl Makefile.PL
make
make test
make install

If you are working with the source repository, then it may not have a Makefile.PL file. But you can use the Dist::Zilla tool in anger to build and install this module:

dzil build
dzil test
dzil install --install-command="cpan ."

For more information, see How to install CPAN modules.

SUPPORT

Only the latest version of this module will be supported.

This module requires Perl v5.20 or later. Future releases may only support Perl versions released in the last ten (10) years.

Reporting Bugs and Submitting Feature Requests

Please report any bugs or feature requests on the bugtracker website https://github.com/robrwo/MooX-Const/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.

If the bug you are reporting has security implications which make it inappropriate to send to a public issue tracker, then see SECURITY.md for instructions how to report security vulnerabilities.

SOURCE

The development version is on github at https://github.com/robrwo/MooX-Const and may be cloned from git://github.com/robrwo/MooX-Const.git

See CONTRIBUTING.md for more information.

AUTHOR

Robert Rothenberg rrwo@cpan.org

This module was inspired by suggestions from Kang-min Liu 劉康民 gugod@gugod.org in a blog post.

CONTRIBUTOR

Kang-min Liu 劉康民 gugod@gugod.org

COPYRIGHT AND LICENSE

This software is Copyright (c) 2018-2026 by Robert Rothenberg.

This is free software, licensed under:

The Artistic License 2.0 (GPL Compatible)

SEE ALSO

MooX::Readonly::Attribute, which has similar functionality to this module.

Const::Fast

Devel::StrictMode

Moo

MooseX::SetOnce

Sub::Trigger::Lock

Types::Const

Type::Tiny