Kata: Open-Closed Principle in Ruby

Last week some friends from Software Craftsmanship Gran Canaria and I practiced doing Matteo Vaccari's Open-Closed Principle kata.

Jose M. Deniz Suarez and I paired to solve it using Ruby.

We got two versions of the code.

These are the tests:

	require_relative '../fizzbuzz'
	describe "FizzBuzz" do
	it "says same number" do
	expect(sayer.say(1)).to eq("1")
	expect(sayer.say(2)).to eq("2")
	end
	it "says Fizz given a multiple of 3" do
	expect(sayer.say(3)).to eq("Fizz")
	expect(sayer.say(6)).to eq("Fizz")
	end
	it "says Buzz given a multiple of 5" do
	expect(sayer.say(5)).to eq("Buzz")
	expect(sayer.say(10)).to eq("Buzz")
	end
	it "says FizzBuzz given a multiple of 3*5" do
	expect(sayer.say(15)).to eq("FizzBuzz")
	expect(sayer.say(30)).to eq("FizzBuzz")
	end
	it "says Bang given a multiple of 7" do
	expect(sayer.say(7)).to eq("Bang")
	expect(sayer.say(14)).to eq("Bang")
	end
	it "says FizzBang given a multiple of 3*7" do
	expect(sayer.say(3*7)).to eq("FizzBang")
	expect(sayer.say(3*7*2)).to eq("FizzBang")
	end
	it "says BuzzBang given a multiple of 5*7" do
	expect(sayer.say(5*7)).to eq("BuzzBang")
	expect(sayer.say(5*7*2)).to eq("BuzzBang")
	end
	it "says FizzBuzzBang given a multiple of 3*5*7" do
	expect(sayer.say(3*5*7)).to eq("FizzBuzzBang")
	expect(sayer.say(3*5*7*2)).to eq("FizzBuzzBang")
	end
	def sayer
	FizzBuzz.new([
	Fizz.new,
	Buzz.new,
	Bang.new,
	SameNumber.new
	])
	end
	end

view raw fizz_buzz_with_reduce_and_template_method_pattern_spec.rb hosted with ❤ by GitHub

and the code of the first version:

	class FizzBuzz
	def initialize sayers
	@sayers = sayers
	end
	def say number
	@sayers.reduce("") do |acc, sayer|
	sayer.say(number, acc)
	end
	end
	end
	class Translator
	def say number, acc
	return add(number, acc) if predicate(number, acc)
	acc
	end
	end
	class SameNumber < Translator
	def add number, acc
	number.to_s
	end
	def predicate number, acc
	acc == ""
	end
	end
	class Fizz < Translator
	def add number, acc
	acc + "Fizz"
	end
	def predicate number, acc
	number % 3 == 0
	end
	end
	class Buzz < Translator
	def add number, acc
	acc + "Buzz"
	end
	def predicate number, acc
	number % 5 == 0
	end
	end
	class Bang < Translator
	def add number, acc
	acc + "Bang"
	end
	def predicate number, acc
	number % 7 == 0
	end
	end

view raw fizz_buzz_with_reduce_and_template_method_pattern.rb hosted with ❤ by GitHub

In this first version, we used a reduce over a list of translators. Each translator might add or not a translation of the given number to the resulting string.

To try something different from what we've tried other times, we used a template method pattern to remove the duplication between the tranlators.

Even though, we reduced the duplication, we didn't like the solution because the resulting Translator interface (public methods) had parameters that were not used by some of its derived classes.

Next, we deleted the code and try another approach. This time we used the decorator pattern.

The tests were the same except for the sayer factory method:

	require_relative '../fizzbuzz'
	describe "FizzBuzz" do
	# ...
	# same tests as in previous version
	# ...
	def sayer
	FizzBuzz.new(Fizz.new(Buzz.new(Bang.new(SameNumber.new))))
	end
	end

view raw fizz_buzz_with_decs_spec.rb hosted with ❤ by GitHub

and this the resulting code:

	class FizzBuzz
	def initialize sayer
	@sayer = sayer
	end
	def say number
	@sayer.say(number, "")
	end
	end
	class SameNumber
	def say number, acc
	return number.to_s if acc == ""
	acc
	end
	end
	class Fizz
	def initialize sayer
	@sayer = sayer
	end
	def say number, acc
	acc += "Fizz" if number % 3 == 0
	@sayer.say(number, acc)
	end
	end
	class Buzz
	def initialize sayer
	@sayer = sayer
	end
	def say number, acc
	acc += "Buzz" if number % 5 == 0
	@sayer.say(number, acc)
	end
	end
	class Bang
	def initialize sayer
	@sayer = sayer
	end
	def say number, acc
	acc += "Bang" if number % 7 == 0
	@sayer.say(number, acc)
	end
	end

view raw fizz_buzz_with_decs.rb hosted with ❤ by GitHub

Then we refactored it to remove some duplication and added a new translation whose condition didn't have to do with being multiple of some number.

This forcer us to generalize the translators passing them a predicate and a translation string through their constructors.

These are the resulting tests (only showing the new test and the sayer factory):

	require_relative '../fizzbuzz'
	describe "FizzBuzz" do
	# ...
	# same tests as in previous versions
	# ...
	it "says hello given 11" do
	expect(sayer.say(11)).to eq("hello")
	end
	def sayer
	FizzBuzz.new(
	Translation.new(
	"hello",
	GivenNumber.new(11),
	Translation.new(
	"Fizz",
	MultipleOf.new(3),
	Translation.new(
	"Buzz",
	MultipleOf.new(5),
	Translation.new(
	"Bang",
	MultipleOf.new(7),
	SameNumber.new
	)
	)
	)
	)
	)
	end
	end

view raw fizz_buzz_with_decs_final_spec.rb hosted with ❤ by GitHub

and code:

https://gist.github.com/trikitrok/619ecabe5ff9f8b08dac

It was a lot of fun.

The constrainsts of this kata are very interesting to practice refactoring and understand the OCP principle.

You can find the code in this GitHub repository.

I'd like to thank Matteo Vaccari for creating it and the great people of Software Craftsmanship Gran Canaria for the fun and the interesting discussions about the different solutions we got.

PS: The "bokata de pata" was also great :)