[Ruby] How to Create Singleton class?

Singleton is one design pattern in the software engineering. Ruby has its own special feature to declare Singleton class. I will demonstrate two examples as below:

Class logger def initialize @ log = file. open ("log.txt", "A") end @ instance = logger. new def self. instance return @ instance end def log (MSG) @ log. puts (MSG) end private_class_method: newend logger. instance. log ('message 1 ')

Require "Singleton" class test include Singleton def idea puts "this is test" End def self. good puts "Good idea" End endputs test. good () puts test. instance. idea ()