Packages Collection.
A Singleton describes an object class that can have only one instance in any
system. An example of a Singleton might be a print spooler or system registry.
This module implements a Singleton class from which other classes can be
derived. By itself, the Class::Singleton module does very little other than
manage the instantiation of a single object. In deriving a class from
Class::Singleton, your module will inherit the Singleton instantiation method
and can implement whatever specific functionality is required.