What is the correct way to write a singleton pattern in Ruby?

Question

I\'m trying to write the most secure singleton in Ruby that I can. I\'m new to the language, which is so elastic that I don\'t have a strong feeling that my singleton class wil

Answer 1

# require singleton lib
require 'singleton'
class AppConfig
  # mixin the singleton module
  include Singleton
  # do the actual app configuration
  def load_config(file)
    # do your work here
    puts "Application configuration file was loaded from file: #{file}"
  end
end

conf1 = AppConfig.instance
conf1.load_config "/home/khelll/conf.yml"
#=>Application configuration file was loaded from file: /home/khelll/conf.yml
conf2 = AppConfig.instance
puts conf1 == conf2
#=>true
# notice the following 2 lines won’t work
AppConfig.new rescue(puts $!)
#=> new method is private
# dup won’t work
conf1.dup rescue(puts $!)
#=>private method `new’ called for AppConfig:Class
#=>can’t dup instance of singleton AppConfig

So what does ruby do when you include the singleton module inside your class?

1. It makes the new method private and so you can’t use it.
2. It adds a class method called instance that instantiates only one instance of the class.

So to use ruby singleton module you need two things:

1. Require the lib singleton then include it inside the desired class.
2. Use the instance method to get the instance you need.