Singleton - Ruby

The Singleton pattern ensures a class has only one instance and provides a global point of access to it. This is useful for managing resources like database connections, configuration settings, or a logger where multiple instances would be detrimental.

The Ruby implementation uses a class variable @@instance to store the single instance. The instance class method acts as the global access point, creating and returning the instance only if it doesn’t already exist. This utilizes Ruby’s meta-programming capabilities and inherent class-level method access, making it a concise and common approach to implementing the Singleton pattern. Defining private_class_method :new prevents direct instantiation outside the class itself.

# singleton.rb

module Singleton
  def self.included(base)
    base.extend(ClassMethods)
  end

  module ClassMethods
    def instance
      @@instance ||= new
    end

    private_class_method :new
  end
end

class Configuration
  include Singleton

  def initialize
    @settings = {
      "api_key" => "your_api_key",
      "timeout" => 30
    }
  end

  def api_key
    @settings["api_key"]
  end

  def timeout
    @settings["timeout"]
  end
end

# Example Usage:
config1 = Configuration.instance
config2 = Configuration.instance

puts config1.object_id == config2.object_id #=> true
puts config1.api_key #=> your_api_key