Programming Ruby 3.3

Singleton

The Singleton design pattern ensures that only one instance of a particular class may be created for the lifetime of a program.

The Singleton module makes this simple to implement. Mix the Singleton module into each class that’s to be a singleton, and that class’s new method will be made private. In its place, users of the class call the method instance, which returns a singleton instance of that class.

Ruby overrides a few other methods of the class when Singleton is mixed in: inherited, clone, _load, and dup, all of which are changed to prevent multiple instances of the class from existing.

In this example, the two instances of MyClass are the same object:

ref_meta_ruby/singleton.rb

require "singleton"

class MyClass
 attr_accessor ...