---
name: "MooseX::Singleton"
section: "3pm"
platform: "linux"
package: "libmoosex-singleton-perl"
version: "0.30-2"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/MooseX::Singleton"
---

# MooseX::Singleton(3pm)

Turn your Moose class into a singleton

## NAME

MooseX::Singleton - Turn your Moose class into a singleton

## VERSION

version 0.30

## SYNOPSIS

```
    package MyApp;
    use MooseX::Singleton;
    has env => (
        is      => 'rw',
        isa     => 'HashRef[Str]',
        default => sub { \%ENV },
    );
    package main;
    delete MyApp->env->{PATH};
    my $instance = MyApp->instance;
    my $same = MyApp->instance;
```

## DESCRIPTION

A singleton is a class that has only one instance in an application. `"MooseX::Singleton"` lets you easily upgrade (or downgrade, as it were) your Moose class to a singleton.

All you should need to do to transform your class is to change `"use Moose"` to `"use MooseX::Singleton"`. This module uses metaclass roles to do its magic, so it should cooperate with most other `"MooseX"` modules.

## METHODS

A singleton class will have the following additional methods:

### Singleton-\>instance

This returns the singleton instance for the given package. This method does *not* accept any arguments. If the instance does not yet exist, it is created with its defaults values. This means that if your singleton requires arguments, calling `"instance"` will die if the object has not already been initialized.

### Singleton-\>initialize(%args)

This method can be called *only once per class*. It explicitly initializes the singleton object with the given arguments.

### Singleton-\>\_clear\_instance

This clears the existing singleton instance for the class. Obviously, this is meant for use only inside the class itself.

### Singleton-\>new

This method currently works like a hybrid of `"initialize"` and `"instance"`. However, calling `"new"` directly will probably be deprecated in a future release. Instead, call `"initialize"` or `"instance"` as appropriate.

## SOME CODE STOLEN FROM

Anders Nor Berle \<debolaz@gmail.com\>

## AND PATCHES FROM

Ricardo SIGNES \<rjbs@cpan.org\>

## SUPPORT

Bugs may be submitted through the RT bug tracker \<https://rt.cpan.org/Public/Dist/Display.html?Name=MooseX-Singleton\> (or bug-MooseX-Singleton@rt.cpan.org \<mailto:bug-MooseX-Singleton@rt.cpan.org\>).

There is also a mailing list available for users of this distribution, at \<http://lists.perl.org/list/moose.html\>.

There is also an irc channel available for users of this distribution, at `"#moose"` on `"irc.perl.org"` \<irc://irc.perl.org/#moose\>.

## AUTHOR

Shawn M Moore \<code@sartak.org\>

## CONTRIBUTORS

- •

  Dave Rolsky \<autarch@urth.org\>

- •

  Karen Etheridge \<ether@cpan.org\>

- •

  Ricardo SIGNES \<rjbs@cpan.org\>

- •

  Kaare Rasmussen \<kaare@jasonic.dk\>

- •

  Anders Nor Berle \<berle@cpan.org\>

- •

  Jonathan Rockway \<jon@jrock.us\>

- •

  Hans Dieter Pearcey \<hdp@weftsoar.net\>

## COPYRIGHT AND LICENSE

This software is copyright (c) 2007 by Shawn M Moore.

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