New idea/example for teaching inheritance, class methods and self in Ruby

lesson.rb

# -------------- INHERITANCE ---------------

class Building # < Object
	def initialize(width, length)
		@width = width
		@length = length
	end

	# Inheritance example
	def has_garden?
		false
	end

	# Super example
	def surface
		@width * @length
	end

	# def to_s; end
end

class House < Building
	def initialize(width, length, address, color)
		super(width, length) # super example
		@address = address
		@color = color
	end

	# Inheritance override example
	def has_garden?
		true
	end

	# Super example
	def surface
		super + 15 # + garden
	end
end

class Castle < Building
	def initialize(width, length, address, butler)
		super(width, length) # super example
		@address = address
		@butler = butler
	end

	# Inheritance override example
	def has_garden?
		true
	end

	# Super example
	def surface
		super + 80 # + big garden
	end
end

class ContainerHouse < Building
	# No difference with the initialize so we don't need it 

	# Inheritance override example
	def has_garden?
		"the world is my garden" # still true though ;) 
	end
end

# ----------------- SELF & CLASS METHODS ----------

class City
	attr_reader :buildings
	def initialize(name)
		@name = name
		@buildings = []
	end

	def add_building(building)
		@buildings << building
	end

	def remove_building(building)
		@buildings.delete(building)
	end

	def to_s
		"#{@name} is a city grand of #{@buildings.length} majestuous buildings."
	end
end

class ContainerHouse < Building
	def self.build_in_city(city, width, length)
		# Create new instance of house
		new_house = ContainerHouse.new(width, length)
		# new_house = self.new(width, length) 

		# Add the building to the city
		city.add_building(new_house) 
	end

	def move_to_city(city)
		# Remove the building from the former city
		@city.remove_building(self)
		# Change the city
		@city = city 
		# Add the building to the new city
		city.add_building(self)
	end
end

paris = City.new("Paris")
dresde = City.new("Dresde")

mobilom = ContainerHouse.build_in_city(paris, width, length)
p paris.buildings
p dresde.buildings

mobilom.move_to_city(dresde)
p paris.buildings
p dresde.buildings