Palestra feita no dia 29/05/2010 no evento Ruby e Rails no Mundo Real.

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

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

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

4. Motivações

5. Muitos programadores
usando Ruby não
sabem usar OO

6. “Raciocínio estático”

7. Linguagem nova, mas
hábitos antigos

8. Organização

9. Modularizar o código

10. Facilitar manutenção

11. Facilitar compreensão
do código para novos
desenvolvedores

12. Design Patterns

13. Motivações

14. Ajudar o Ruby a ser
“Enterprise”

15. Patterns implementados X Enterprisy

16. YAGNI

17. Um exemplo simples...

18. 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

19. 1 class Bhaskara
2 end

20. 1 class Bhaskara
2 def initialize(a, b, c)
3 @a, @b, @c = a, b, c
4 end
5 end

21. 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

22. 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

23. 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

24. O que eu preciso para
refatorar?

25. TESTES

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

27. 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

28. 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

29. 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

30. 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

31. 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

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

33. 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

34. 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 # ...

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

36. 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'

37. 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 )

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

39. 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

40. 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

41. 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

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

43. 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

44. 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

45. Delegue, delegue, delegue...

46. 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

47. O Ruby pode dar uma
ajudinha...

48. 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

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

50. 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

51. 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

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

53. 1 class Circle
2 def area
3 3.14159265 * (r ** 2)
4 end
5 end

54. 1 class Circle
2 PI = 3.14159265
3
4 def area
5 PI * (r ** 2)
6 end
7 end

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

56. 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

57. 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

58. 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))

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

60. 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

61. 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...

62. 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

63. Simplifique expressões
condicionais

64. 1 if product.release_date < 3.months.ago || quantity > 100
2 self.value *= 0.90
3 end

65. 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

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

67. 1 if age > 40
2 if gender == :male
3 if last_visit > 1.month.ago
4 # ...
5 end
6 end
7 end

68. 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...

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

70. 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

71. 1 class Bicycle
2 def press_brake(brake)
3 brakes[brake].press
4 end
5 end

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

73. 1 def do_something(target)
2 target.prepare rescue nil
3 target.explode
4 end

74. 1 def do_something(target)
2 target.prepare if target.respond_to? :prepare
3 target.explode
4 end

75. Herança

76. 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

77. 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

78. Strategy

79. 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

80. 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

81. 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

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

83. 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

84. Use quando você precisar
alterar o algorítmo em
tempo de execução

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

86. 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

87. ctrl-z ?

88. 1 class Command
2 attr_reader :description
3
4 def initialize(description)
5 @description = description
6 end
7 end

89. 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

90. 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

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

92. Proxy

93. 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

94. 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

95. 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

96. Perguntas?

97. Obrigado!