class SingletonCvar

  def self.instance
    @@instance ||= new
  end
  private_class_method :new

end

singleton = SingletonCvar.instance
singleton_again = SingletonCvar.instance
p singleton.object_id # => 70235617244200
p singleton_again.object_id # => 70235617244200

SingletonCvar.new
# singleton_cvar.rb:15:in `<main>': private method `new' called
# for SingletonCvar:Class (NoMethodError)