food.rb

class FoodException < Exception
end

class Food
  attr_reader :type
  
  def initialize(type)
    @type = type
  end
end

class Diet
  def initialize(acceptable_foods)
    @acceptable_foods = acceptable_foods
  end
  
  def ensure_edible(food)
    raise FoodException.new unless @acceptable_foods.include? food.type
  end
end

class Animal
  def initialize(stomach, diet)
    @stomach = stomach
    @diet = diet
  end
  
  def eat(food)
    begin
      @diet.ensure_edible(food)
      @stomach.eat(food)
      puts "Yum"
    rescue FoodException => e
      puts "Yuck"
    end
  end
end

class Stomach
  SMALL = 3
  MEDIUM = 5
  LARGE = 8
  
  def initialize(size)
    @size = size
    @food = []
  end
  
  def eat(food)
    raise FoodException.new if @food.length >= size
    @food << food
    end
  end
end

HerbivoreDiet = Diet.new([:vegtable, :fruit])

small_herbivore = Animal.new(Stomach.new(Stomach::SMALL), HerbivoreDiet))