shvets / design_patterns_in_ruby

# singleton.rb
 
# Ensure a class only has one instance and provide a global point of access to it.
 
# Note: try to avoid singleton (see singleton-corrected.rb). 
# Major question: how to test/mock the singleton?
 
class MySingleton1
  @@instance = nil
 
  def self.instance()
    if @@instance == nil
      public_class_method :new # enables instance creation for this class
 
      @@instance = new() unless @@instance
 
      private_class_method :new # disable instance creation for this class
    end
 
    @@instance
  end
 
  private_class_method :new # disable instance creation for this class
end
 
require 'singleton'
 
class MySingleton2
  include Singleton
end
 
# MySingleton1.new # error
 
puts "singleton1: " + MySingleton1.instance.to_s
puts "singleton1: " + MySingleton1.instance.to_s
 
puts "singleton2: " + MySingleton2.instance.to_s
puts "singleton2: " + MySingleton2.instance.to_s