Design Patterns the Ruby way: proxy

design_patterns_proxy.rb

####### PROXY PATTERN #############

### way #1
## The following code implements the proxy pattern in the traditional
## manner, i.e. the proxy mirrors the methods of the real object (e.g
## drive) and delegates accordingly

class RealCar
	def drive
		puts "vroom,vroom..."
	end
end

class ProxyCar
	def initialize(real_car, driver_age)
		@driver_age = driver_age
		@real_car = real_car
	end

	def drive
		car = get_real_car
		check_access ? car.drive : puts("Sorry, you're too young to drive")
	end

	def check_access
		@driver_age > 16
	end

	def get_real_car
		@real_car || (@real_car = Car.new(@driver_age))
	end
end

## this is the client for our proxy. When it calls the drive method
## we're going to give it our proxy to drive instead of the real car
class Client
	attr_reader :age

	def initialize(age)
		@age = age
	end

	def drive(car)
		car.drive
	end
end



tom = Client.new(15)

car = RealCar.new()
proxy = ProxyCar.new(car, tom.age)

tom.drive(proxy)

### way #2
## The following code uses dynamic dispatching in our Proxy, so we
## capture any method call to our Proxy via #method_missing and
## re-direct it to the real object

#remove previous definition of ProxyCar
Object.send(:remove_const, :ProxyCar)

class ProxyCar
	def initialize(real_car, driver_age)
		@driver_age = driver_age
		@real_car = real_car
	end

	def method_missing(name, *args)
		car = get_real_car
		check_access ? car.send(name, *args) : puts("Sorry, can't do this")
	end

	def check_access
		@driver_age > 16
	end

	def get_real_car
		@real_car || (@real_car = Car.new(@driver_age))
	end
end

## we create and use our client and proxy in the same way as before,
## even though we're using dynamic dispatching in our proxy

jerry = Client.new(25)

car = RealCar.new()
proxy = ProxyCar.new(car, jerry.age)

jerry.drive(proxy)