Favorite Refactoring Techniques: Extract Functions

The next refactoring technique we'll look at is extracting behavior into functions. Say we have the following example:

	class SubwayTrain
	attr_accessor :averageSpeed, :subwayCar, :speed, :subwayCars
	def initialize
	self.averageSpeed = 17
	self.speed = 0;
	self.subwayCars = [];
	end
	def allowPassengersOnBoard
	puts "Train arriving at station."
	while(speed > 0)
	self.speed -= 1
	end
	puts "Train Stopped."
	puts "Doors Open."
	subwayCars.each do | subwayCar |
	subwayCar.open()
	end
	sleep 1
	subwayCars.each do | subwayCar |
	subwayCar.close()
	end
	puts "Stand Clear of the Closing Doors"
	while(speed < averageSpeed)
	self.speed += 1
	end
	puts "Train leaving station."
	end
	end
	train = SubwayTrain.new
	train.speed = 100;
	train.allowPassengersOnBoard()

view raw move_and_extract_function_example.rb hosted with ❤ by GitHub

SubwayTrain#processStop has a lot of behavior. The intention could be made clearer by separating each behavior into its own method. The behavior we extract will also become available to other classes that may need it, outside of the context of getting passengers at a subway station.

After extracting the behavior, #processStop looks like this:

	class SubwayTrain
	attr_accessor :averageSpeed, :subwayCar, :speed, :subwayCars
	def initialize
	self.averageSpeed = 17
	self.speed = 0;
	self.subwayCars = [];
	end
	def allowPassengersOnBoard
	puts "Train arriving at station."
	slowDownToHalt
	puts "Train Stopped."
	openDoors
	puts "Doors Open."
	sleep 1
	puts "Stand Clear of the Closing Doors"
	increaseSpeedToAverageSpeed
	puts "Train leaving station."
	end
	def slowDownToHalt
	while(speed > 0)
	self.speed -= 1
	end
	end
	def openDoors
	subwayCars.each do | subwayCar |
	subwayCar.close()
	end
	end
	def increaseSpeedToAverageSpeed
	while(speed < averageSpeed)
	self.speed += 1
	end
	end
	end
	train = SubwayTrain.new
	train.speed = 100;
	train.allowPassengersOnBoard

view raw move_and_extract_function_example_extraction.rb hosted with ❤ by GitHub