How do I create a Class using the Singleton Design Pattern in Ruby?

Question

The singleton pattern is a design pattern that is used to restrict instantiation of a class to one object instance. Although I know how to code the singleton pattern in C++ and Java, I was wondering if anyone know how to implement it in Ruby?

Answer 1

Use the singleton module:

class Clazz
  include Singleton
end

See http://www.ruby-doc.org/stdlib/libdoc/singleton/rdoc/index.html for more info.

Answer 2

Actually, the above answer was not completely correct.

require 'singleton'

class Example
  include Singleton
end

You also need to include the require 'singleton' statement.

Answer 3

You could use modules to the same effect I believe, although its not "the singleton pattern" you can have global state that way (which is what a singleton is ! Naughty global state !).