Refatoração + Design Patterns em Ruby

Refatorando Ruby Técnicas de Orientação a Objetos e Design Patterns Aplicados a Linguagens Dinâmicas Cássio Marques Ruby e Rails no Mundo Real 2010

cassiomarques.wordpress.com @cassiomarques cassiommc@gmail.com

http://www.ﬂickr.com/photos/docman/ Refatoração

Motivações

Muitos programadores usando Ruby não sabem usar OO

“Raciocínio estático”

Linguagem nova, mas hábitos antigos

Organização

Modularizar o código

Facilitar manutenção

Facilitar compreensão do código para novos desenvolvedores

Design Patterns

Motivações

Ajudar o Ruby a ser “Enterprise”

Patterns implementados X Enterprisy

Um exemplo simples...

1 class Bhaskara 2 def solve(a, b, c) 3 # Calcula o delta 4 d = b ** 2 - 4 * a * c 5 6 if d < 0 7 puts 'Raízes complexas - Não sei resolver!' 8 else 9 # calculando raízes 10 r1 = (-b + Math.sqrt(d))/(2.0 * a) 11 r2 = (-b - Math.sqrt(d))/(2.0 * a) 12 13 # imprimindo resultados 14 puts "Raiz 1: #{r1}" 15 puts "Raiz 2: #{r2}" 16 end 17 end 18 end

1 class Bhaskara 2 end

1 class Bhaskara 2 def initialize(a, b, c) 3 @a, @b, @c = a, b, c 4 end 5 end

1 class Bhaskara 2 def initialize(a, b, c) 3 @a, @b, @c = a, b, c 4 end 5 6 private 7 def delta 8 @b ** 2 - 4 * @a * @c 9 end 10 11 def solve 12 @r1 = (-@b + Math.sqrt(delta))/(2.0 * @a) 13 @r2 = (-@b - Math.sqrt(delta))/(2.0 * @a) 14 end 15 end

1 class Bhaskara 2 def initialize(a, b, c) 3 @a, @b, @c = a, b, c 4 end 5 6 def print_results 7 if delta < 0 8 puts 'Raízes complexas - Não sei resolver!' 9 else 10 solve 11 puts "Raiz 1: #{@r1}" 12 puts "Raiz 2: #{@r2}" 13 end 14 end 15 16 private 17 def delta 18 @b ** 2 - 4 * @a * @c 19 end 20 21 def solve 22 @r1 = (-@b + Math.sqrt(delta))/(2.0 * @a) 23 @r2 = (-@b - Math.sqrt(delta))/(2.0 * @a) 24 end 25 end

1 class Bhaskara 2 def initialize(a, b, c) 3 @a, @b, @c = a, b, c 4 end 5 6 def print_results 7 delta < 0 ? print_complex_results : print_real_results 8 end 9 10 private 11 def delta 12 @b ** 2 - 4 * @a * @c 13 end 14 15 def solve 16 @r1 = (-@b + Math.sqrt(delta))/(2.0 * @a) 17 @r2 = (-@b - Math.sqrt(delta))/(2.0 * @a) 18 end 19 20 def print_real_results 21 solve 22 puts "Raiz 1: #{@r1}" 23 puts "Raiz 2: #{@r2}" 24 end 25 26 def print_complex_results 27 puts 'Raízes complexas - Não sei resolver!' 28 end 29 end

O que eu preciso para refatorar?

TESTES

Mantenha seus métodos pequenos http://www.ﬂickr.com/photos/davidden/

1 class ShoppingCart 2 def total_value 3 total = 0 4 for item in @items 5 sub_total = item.value * item.quantity 6 if item.quantity > 3 7 sub_total *= 0.90 8 elsif item.quantity > 6 9 sub_total *= 0.85 10 elsif item.quantiy > 9 11 sub_total *= 0.80 12 end 13 total += sub_total 14 end 15 total 16 end 17 end

1 # - Elimina variáveis temporárias em favor de métodos 2 class ShoppingCart 3 def total_value 4 total = 0 5 for item in @items 6 total += if item.quantity > 3 7 sub_total(item) * 0.90 8 elsif item.quantity > 6 9 sub_total(item) * 0.85 10 elsif item.quantiy > 9 11 sub_total(item) * 0.80 12 end 14 end 15 total 16 end 17 18 def sub_total(item) 19 item.value * item.quantity 20 end 21 end 22

1 # - Método usa apenas atributos de outro objeto 2 # => Mover! 3 class ShoppingCart 4 def total_value 5 total = 0 6 for item in @items 7 total += if item.quantity > 3 8 item.total_value * 0.90 9 elsif item.quantity > 6 10 item_total_value * 0.85 11 elsif item.quantiy > 9 12 item.total_value = 0.80 13 end 14 end 15 total 16 end 17 end 18 19 class Item 20 def total_value 21 @value * @quantity 22 end 23 end

1 # - Método fazendo coisa demais 2 # => Extrair! 3 class ShoppingCart 4 def total_value 5 total = 0 6 for item in @items 7 total += item.total_value * discount(item.quantity) 8 end 9 total 10 end 11 12 def discount(quantity) 13 case quantity 14 when (1..2); 1.00 15 when (3..5); 0.90 16 when (6..8); 0.85 17 else 0.80 18 end 19 end 20 end

1 # - Use Ruby! 2 class ShoppingCart 3 def total_value 4 items.inject(0.0) { |sum, item| 5 sum += item.total_value * discount(item.quantity) 6 } 7 end 8 9 def discount(quantity) 10 case quantity 11 when (1..2); 1.00 12 when (3..5); 0.90 13 when (6..8); 0.85 14 else 0.80 15 end 16 end 17 end

Faça objetos se comportarem como coleções http://www.ﬂickr.com/photos/deepsignal/366774303/sizes/l/

1 class Library 2 def search_book_by_title(title) 3 @books.select { |book| book.title == title } 4 end 5 6 def search_book_by_author(author) 7 @books.select { |book| book.author == author } 8 end 9 10 def sort_by_title 11 @books.sort_by { |book| book.title } 12 end 13 14 def authors 15 @books.map { |book| book.author } 16 end 17 18 # ... 19 end

1 class Library 2 include Enumerable 3 4 def each 5 @books.each { |book| yield book } 6 end 7 end 8 9 library.each { |book| ... } 10 library.inject { |book| ... } 11 library.map { |book| ... } 12 library.sort { |book| ... } 13 # ...

Dê nomes aos parâmetros dos métodos http://www.ﬂickr.com/photos/giantginkgo/

1 class Dialog 2 def initialize(height, width, name, title) 3 @height = height 4 @width = width 5 @name = name 6 @title = title 7 end 8 end 9 10 dialog = Dialog.new 200, 400, 'dialog1', 'A Dialog'

1 class Dialog 2 def initialize(options) 3 @height = options[:height] 4 @width = options[:width] 5 @name = options[:name] 6 @title = options[:title] 7 end 8 end 9 10 dialog = Dialog.new( 11 :height => 200, 12 :width => 400, 13 :name => 'dialog1', 14 :title => 'A Dialog' 15 )

Anotações http://www.ﬂickr.com/photos/matski_98/

1 class Person 2 def state=(state) 3 unless [:sick, :healthy].include?(state) 4 raise ArgumentError, "unknown state: #{state}" 5 end 6 @state = state 7 end 8 end 9 10 class Vehicle 11 def state=(state) 12 unless [:parked, :running].include?(state) 13 raise ArgumentError, "unknown state: #{state}" 14 end 15 @state = state 16 end 17 end

1 module HasStates 2 def has_states(*args) 3 define_method :state= do |new_state| 4 unless args.include?(new_state) 5 raise ArgumentError, "unknown state: #{state}" 6 end 7 @state = new_state 8 end 9 end 10 end

1 class Person 2 extend HasStates 3 4 has_states :sick, :healthy 5 end 6 7 class Vehicle 8 extend HasStates 9 10 has_states :parked, :running 11 end 12 13 Object.extend HasStates

Uma classe não deve realizar trabalhos que não lhe pertencem...

1 class Person 2 attr_accessor :telephone_number, :telephone_area_code 3 4 def formatted_telephone 5 "(#{telephone_area_code}) #{telephone_number}" 6 end 7 end

1 class Person 2 def initialize 3 @telephone_number = TelephoneNumber.new 4 end 5 end 6 7 class TelephoneNumber 8 attr_accessor :area_code, :number 9 10 def formatted 11 "(#{area_code}) #{number}" 12 end 13 end

Delegue, delegue, delegue...

1 class Queue 2 def initialize 3 @queue = [] 4 end 5 6 def enqueue(element) 7 @queue.unshift element 8 end 9 10 def dequeue 11 @queue.pop 12 end 13 end

O Ruby pode dar uma ajudinha...

1 require 'forwardable' 2 3 class Queue 4 extend Forwardable 5 6 def initialize 7 @queue = [] 8 end 9 10 def_delegator :@queue, :unshift, :enqueue 11 def_delegator :@queue, :pop, :dequeue 12 end

Não exponha o interior de seus objetos sem necessidade http://www.ﬂickr.com/photos/mwichary/

1 class Room 2 attr_reader :air_conditioner 3 end 4 5 class AirConditioner 6 attr_reader :sensor 7 end 8 9 class TemperatureSensor 10 def temperature 11 #... 12 end 13 end 14 15 if room.air_conditioner.sensor.temperature > 28 16 room.air_conditioner.on 17 end

1 class Room 2 attr_reader :air_conditioner 3 4 def temperature 5 air_conditioner.sensor.temperature 6 end 7 end 8 9 if room.temperature > 28 10 room.air_conditioner.on 11 end

Substitua números mágicos por constantes http://decluttr.com/4524127771_white

1 class Circle 2 def area 3 3.14159265 * (r ** 2) 4 end 5 end

1 class Circle 2 PI = 3.14159265 3 4 def area 5 PI * (r ** 2) 6 end 7 end

Encapsule coleções de objetos http://www.ﬂickr.com/photos/eagleglide/

1 class Cart 2 attr_accessor :products 3 end 4 5 class Product 6 attr_reader :value, :name 7 8 def initialize(name, value) 9 @name, @value = name, value 10 end 11 end

1 products = [] 2 products << Product.new('Camiseta', 35.00) 3 products << Product.new('Bermuda', 38.00) 4 products << Product.new('Boné', 20.00) 5 cart = Cart.new 6 cart.products = products 7 cart.products.pop # => alterei o estado do carrinho

1 class Cart 2 def initialize 3 @products = [] 4 end 5 6 def add_product(product) 7 @products << product 8 end 9 10 def remove_product(product) 11 @products.delete product 12 end 13 end 14 15 cart = Cart.new 16 cart.add_product(Product.new('Camiseta', 35.00))

Substitua condicionais por polimorﬁsmo http://www.ﬂickr.com/photos/randyread/

1 class Tax 2 def initialize(type, value) 3 @type = type 4 @value = value 5 end 6 7 def retained_value 8 case @type 9 when :irpj; @value * 0.015 10 when :pis; @value * 0.0065 11 when :cofins; @value * 0.030 12 when :iss; 0.0 13 end 14 end 15 16 def due_value 17 case @type 18 when :irpj; @value * 0.033 19 when :pis; 0.0 20 when :cofins; 0.0 21 when :iss; @value * 0.02 22 end 23 end 24 end

1 module Tax 2 def due_value 3 @due_rate * @value 4 end 5 6 def retained_value 7 @retained_rate * @value 8 end 9 end 10 11 class IrpjTax 12 include Tax 13 14 def initialize(value) 15 @value = value 16 @due_rate = 0.033 17 @retained_rate = 0.015 18 end 19 end 20 21 # o mesmo para as demais classes...

1 class Invoice 2 def initialize(value) 3 @value = value 4 create_taxes 5 end 6 7 def add_tax(tax) 8 @taxes << tax 9 end 10 11 def total_taxes_value 12 @taxes.inject(0.0) { |sum, tax| 13 sum += tax.due_value + tax.retained_value 14 } 15 end 16 17 private 18 def create_taxes 19 @taxes = [] 20 @taxes << IrpjTax.new(@value) 21 @taxes << PisTax.new(@value) 22 @taxes << CofinsTax.new(@value) 23 @taxes << IssTax.new(@value) 24 end 25 end 26 27 invoice = Invoice.new 1400.00 28 puts invoice.total_taxes_value

Simpliﬁque expressões condicionais

1 if product.release_date < 3.months.ago || quantity > 100 2 self.value *= 0.90 3 end

1 if elegible_for_discount? 2 self.value *= 0.90 3 end 4 5 def elegible_for_discount? 6 old? && great_quantity? 7 end 8 9 def old? 10 product.release_date < 3.months.ago 11 end 12 13 def great_quantity? 14 quantity > 100 15 end

http://www.ﬂickr.com/photos/jeff_oliver/ Mas uma expressão condicional pode ser melhor que ifs aninhados...

1 if age > 40 2 if gender == :male 3 if last_visit > 1.month.ago 4 # ... 5 end 6 end 7 end

1 if age > 40 && gender == :male && last_visit > 1.month 2 # ... 3 end 4 5 # e a partir daqui podemos extrair as condições para 6 # métodos...

Às vezes faz mais sentido juntar do que separar...

1 class Bicycle 2 def press_front_brake 3 brakes[:front].press 4 end 5 6 def press_rear_brake 7 brakes[:rear].press 8 end 9 end

1 class Bicycle 2 def press_brake(brake) 3 brakes[brake].press 4 end 5 end

Veriﬁque se a mensagem pode ser enviada http://www.ﬂickr.com/photos/funtik/

1 def do_something(target) 2 target.prepare rescue nil 3 target.explode 4 end

1 def do_something(target) 2 target.prepare if target.respond_to? :prepare 3 target.explode 4 end

Herança

1 class CdPlayer 1 class TapeDeck 2 def turn_on 2 def turn_on 3 @on = true 3 @on = true 4 end 4 end 5 5 6 def turn_off 6 def turn_off 7 @on = false 7 @on = false 8 end 8 end 9 9 10 def play 10 def play 11 play_disc 11 play_tape 12 end 12 end 13 end 13 end

1 class AudioDevice 2 def turn_on 3 @on = true 4 end 5 6 def turn_off 7 @on = false 8 end 9 end 10 11 class CdPlayer < AudioDevice 12 def play 13 play_disk 14 end 15 end 16 17 class TapeDeck < AudioDevice 18 def play 19 play_tape 20 end 21 end

Strategy

1 class Text 2 attr_reader :contents 3 4 def left_aligned_format 5 # ... 6 end 7 8 def right_aligned_format 9 # ... 10 end 11 12 def justified_format 13 # ... 14 end 15 end

1 class LeftAlignedFormatter 2 def format(context) 3 align_left context.contents 4 end 5 end 6 7 class RightAlignedFormatter 8 def format(context) 9 align_right context.contents 10 end 11 end 12 13 class RightJustifiedFormatter 14 def format(context) 15 justify context.contents 16 end 17 end

1 class Text 2 attr_reader :contents 3 attr_accessor :formatter 4 5 def initialize(contents, formatter) 6 @contents, @formatter = contents, formatter 7 end 8 9 def format 10 @formatter.format self 11 end 12 end

Blocos, ao resgate! http://www.ﬂickr.com/photos/bekahstargazing/

1 class Text 2 attr_reader :contents 3 attr_accessor :formatter 4 5 def initialize(contents, &formatter) 6 @contents, @formatter = contents, formatter 7 end 8 9 def format 10 @formatter.call self 11 end 12 end 13 14 left_aligned_text = Text.new 'some text' do |context| 15 align_left context.contents 16 end

Use quando você precisar alterar o algorítmo em tempo de execução

http://www.ﬂickr.com/photos/micahdowty/

1 class Document 2 def change_text_color(color) 3 @text.color = color 4 end 5 6 def change_background_color(color) 7 @text.background_color = color 8 end 9 10 def change_font_size(size) 11 @text.font_size = size 12 end 13 14 def change_font(font) 15 @text.font = font 16 end 17 end

ctrl-z ?

1 class Command 2 attr_reader :description 3 4 def initialize(description) 5 @description = description 6 end 7 end

1 class ChangeTextColorCommand < Command 2 def initialize(target) 3 super("Altera a cor do texto") 4 @target = target 5 end 6 7 def execute(color) 8 @old_color = @target.text.color 9 @target.text.color = color 10 end 11 12 def unexecute 13 @target.text.color = @old_color if @old_color 14 end 15 end

1 class Document 2 def initialize 3 @commands = [] 4 end 5 6 def change_text_color(color) 7 run_command ChangeTextColorCommand.new(self), color 8 end 9 10 def change_font(font) 11 run_command ChangeFontCommand.new(self), font 12 end 13 14 def undo_last_action 15 @commands.pop.unexecute unless @commands.empty? 16 end 17 18 private 19 def run_command(command, param) 20 command.execute param 21 @commands << command 22 end 23 end

Use quando você precisar realizar tarefas especíﬁcas e mantê-las em um registro

1 class Task 2 def initialize(creator) 3 @creator = creator 4 end 5 6 def owner=(owner) 7 @owner = owner 8 end 9 10 def add_comment(comment) 11 @comments << comment 12 end 13 14 def update_description(new_description) 15 @description = description 16 end 17 18 def close 19 @status = :closed 20 end 21 end

1 class TaskProtectionProxy 2 def initialize(target) 3 @target = target 4 end 5 6 def owner=(owner) 7 check_permissions :owner= 8 @owner = owner 9 end 10 11 def add_comment(comment) 12 check_permissions :add_comment 13 @comments << comment 14 end 15 16 # ... 17 18 private 19 def check_permissions(what) 20 unless can_do?(current_user, what) 21 raise 'Acesso negado!' 22 end 23 end 24 end

1 class TaskProtectionProxy 2 def initialize(target) 3 @target = target 4 end 5 6 def method_missing(method, *args) 7 check_permissions(method) 8 @target.send method, args 9 end 10 11 private 12 def check_permissions(what) 13 unless can_do?(current_user, what) 14 raise 'Acesso negado!' 15 end 16 end 17 end

Perguntas?

Obrigado!

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Refatoração + Design Patterns em Ruby

by cassiomarques on May 30, 2010

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Refatoração + Design Patterns em Ruby — Presentation Transcript