add ruby version singleton pattern

src/observer/ruby/car.rb

@@ -0,0 +1,30 @@
+require 'observer'
+
+class Notifier
+	def update(car, miles)
+		puts "The car has logged #{miles} miles, totaling #{car.mileage} miles traveled."
+		puts "The car needs to be taken in for a service!" if car.service \
+			< car.mileage
+	end
+end
+
+class Car
+	include Observable
+	attr_reader :mileage, :service
+
+	def initialize(mileage = 0, service = 3000)
+		@mileage, @service = mileage, service
+		add_observer(Notifier.new)
+	end
+
+	def log(miles)
+		@mileage += miles
+		changed
+		notify_observers(self, miles)
+	end
+end
+
+car = Car.new(2300, 3000)
+car.log(100)
+car.log(354)
+car.log(300)

src/observer/ruby/notifier.rb

@@ -0,0 +1,9 @@
+class Notifier
+	def update(car, miles)
+		puts "The car has logged #{miles} miles, totaling #{car.mileage}
+		miles traveled."
+		puts "The car needs to be taken in for a service!" if car.service
+		&< car.mileage
+		&amp;lt;= car.mileage
+	end
+end

src/observer/ruby/test.rb

@@ -0,0 +1,3 @@
+#!/usr/bin/env ruby
+
+require 'Car'