MooseX::SingletonMethod

MooseX::SingletonMethod is a Perl module that offers Singleton methods in Moose, either directly or through a role. The module is easy to use, as showcased by the simple example below.

To begin, you must import the module and create a new package. Then create an instance of the package to which you want to add a Singleton method. In the example below, the package is called "Baz."

# Simple usage example....
package Baz;
use MooseX::SingletonMethod; # new;
my $foo = Baz->new;

The Singleton method can be added to the instance using the add_singleton_method function. The example below shows how to add a Singleton method called "baz" to $baz.

$baz->add_singleton_method( baz => sub { 'baz!' } );

Once the method is added, you can call it as shown below.

say $baz->baz; # => 'baz'

However, calling the method on the package itself generates an error.

say $foo->baz; # ERROR: Can't locate object method "baz"....

To avoid this, you should use the MooseX::SingletonMethod::Role instead of MooseX::SingletonMethod. To apply the role, modify your package as shown below.

package Baz;
use Moose;
with 'MooseX::SingletonMethod::Role';
no Moose;.

Overall, MooseX::SingletonMethod is an excellent module for adding Singleton methods to Moose. Whether you use the module directly or via a role, it is easy to use, and the impact on your code will be noticeable.