Example of using Observable in Ruby

obervable_example.rb

require 'observer'

class CoffeeShop
  include Observable
  attr_reader :customers

  def initialize(name, capacity)
    @name = name
    @capacity = capacity
    @customers = []
  end

  def enter(customer)
    unless full?
      changed
      @customers.push(customer)
      notify_observers(Time.now)
    end
  end

  def depart(customer)
    unless empty?
      changed
      @customers.delete(customer)
      notify_observers(Time.now)
    end
  end

  def full?
    @customers.count >= @capacity
  end

  def empty?
    @customers.count.zero?
  end
end

class CoffeeShopObserver
  def initialize(shop)
    @shop = shop
    @shop.add_observer(self)
  end
end

class CoffeeShopEmptyObserver < CoffeeShopObserver
 def update(time)
    if @shop.empty?
      puts "#{time}: The shop is EMPTY so some staff can go home."
    end
  end
end

class CoffeeShopFullObserver < CoffeeShopObserver
  def update(time)
    if @shop.full?
      puts "#{time}: The shop is FULL - quick call more staff!"
    end
  end
end

usage.rb

coffee_shop = CoffeeShop.new("Costa", 3)
CoffeeShopEmptyObserver.new(coffee_shop)
CoffeeShopFullObserver.new(coffee_shop)

potential_customers = %w(Bob Harry William Darren Brian Susan Kelly John Kevin)
customer_actions = [:enter, :enter, :depart] #enter in twice to try and encourage more customers!

20.times do
  action = customer_actions.sample

  if action == :enter
    customer = potential_customers.sample
    potential_customers.delete(customer)
    puts "Entering: #{customer}"
    coffee_shop.enter(customer)
  else
    unless coffee_shop.empty?
      customer = coffee_shop.customers.sample
      puts "Leaving #{customer}"
      potential_customers.push(customer)
      coffee_shop.depart(customer)
    end
  end
  sleep 0.1
end