singleton in ruby

What is Singleton?

singleton is a way to “ensure a class only has one instance, and provide a global point of access to it”

WIKI: singleton pattern

the singleton pattern is a software design pattern that restricts the instantiation of a class to one object

You can achieve the singleton using class initialization private or using singleton module.

Singleton module gives a broader implementation by achieving the following things:

1. Making Klass.new and Klass.allocate private.
2. Overriding Klass.inherited(sub_klass) and Klass.clone() to ensure that the Singleton properties are kept when inherited and cloned.
3. Providing the Klass.instance() method that returns the same object each time it is called.
4. Overriding Klass._load(str) to call Klass.instance().
5. Overriding Klass#clone and Klass#dup to raise TypeErrors to prevent cloning or duping.

Here a simple code snippet to make a singleton class, but you can always use singleton module](https://www.rubydoc.info/stdlib/singleton/Singleton)

# minimal example for singleton pattern
class Configs
  class << self
    def instance
      @instance ||= new
    end
    
    private :new
  end
end


# using singleton module
require 'singleton'
class Config
  include Singleton
end