Eastward HO!

1. EASTWARD
   HO! A clear path with OO Jim Gay / @saturnflyer
3. EAST ORIENTED
4. EAST ORIENTED James Ladd
6. COMMANDS QUERIES
7. EAST WEST
8. RULE 1 ALWAYS RETURN SELF
9. RULE 2 OBJECTS MAY QUERY
 THEMSELVES
10. RULE 3 FACTORIES ARE EXEMPT
11. FANCY WORDS
12. FANCY WORDS POLYMORPHISM
13. FANCY WORDS ENCAPSULATION
14. FANCY WORDS COUPLING
15. FANCY WORDS IDEMPOTENT
16. IF
17. IF ELSIF ELSIF ELSIF ELSIF
18. CASE WHEN WHEN WHEN WHEN
19. IF
20. IF IF IF IF IF IF IF IF IF IF IF IF IF
21. class Person! attr_reader :address! end!
22. class Person! attr_reader :address! ! def display_address! ! end! end!
23. class Person! attr_reader :address! ! def display_address! ! end! end! "123 Main St. Arlington" ! "123 Main St. VA 22222" "123 Main St. Arlington, VA 22222” ! "Arlington, VA"
24. class Person! attr_reader :address! ! def display_address! ! end! end! "123 Main St. Arlington" ! "123 Main St. VA 22222" "123 Main St. Arlington, VA 22222” ! "Arlington, VA"
25. class Person! def display_address! "".tap do |string|! if !address.street.nil? || !address.street.empty?! string << address.street! end! ! string << "\n" unless string.empty?! ! if !address.city.nil? address.city.empty? || address.city.nil?! string << address.city! end! ! if address.province || address.postal_code! string << ", "! end! ! if address.province || address.postal_code! if address.province! string << address.province! end! ! string << " "! ! "123 Main St. Arlington" ! "123 Main St. VA 22222" "123 Main St. Arlington, VA 22222” ! "Arlington, VA"
26. RULE 1 ALWAYS RETURN SELF
27. class Person! def display_address! ! ! ! ! ! ! ! # … all the code …! ! ! ! ! ! ! ! ! ! ! self! end! end! "123 Main St. Arlington" ! "123 Main St. VA 22222" "123 Main St. Arlington, VA 22222” ! "Arlington, VA" RULE 1
28. class Person! def display_address! ! ! ! ! ! ! ! # … all the code …! ! ! ! ! ! ! ! ! ! ! self! end! end! "123 Main St. Arlington" ! "123 Main St. VA 22222" "123 Main St. Arlington, VA 22222” ! "Arlington, VA"
29. Tell,
    Don’t Ask
30. Tell,
    Don’t Ask Andy Hunt and 
 Dave Thomas
31. Tell,
    Don’t Ask ensure a correct 
 division of responsibility that places the right functionality in the 
 right class 
 without causing 
 excess coupling 
 to other classes. Andy Hunt and 
 Dave Thomas
32. Tell,
    Don’t Ask ensure a correct 
 division of responsibility that places the right functionality in the 
 right class 
 without causing 
 excess coupling 
 to other classes. Andy Hunt and 
 Dave Thomas
33. Command,
    Don’t Query
34. street
    street?
35. street
    street?
36. Command,
    Don’t Query ! ! ! if !address.street.nil? || !address.street.empty?! string << address.street! end
37. Command,
    Don’t Query ! ! ! if !address.street.nil? || !address.street.empty?! string << address.street! end
38. Command,
    Don’t Query ! ! ! if !address.street.nil? || !address.street.empty?! string << address.street! end
39. Command,
    Don’t Query ! ! ! if !address.street.nil? || !address.street.empty?! string << address.street! end
40. class Person! def display_address! "".tap do |string|! if !address.street.nil? || !address.street.empty?! string << address.street! end! ! string << "\n" unless string.empty?! ! if !address.city.nil? address.city.empty? || address.city.nil?! string << address.city! end! ! if address.province || address.postal_code! string << ", "! end! ! if address.province || address.postal_code! if address.province! string << address.province! end! ! string << " "! !
41. The Pretty Good Idea of Demeter
42. The Pretty Good Idea of Demeter ! ! ! if !address.street.nil? || !address.street.empty?! string << address.street! end
43. The Pretty Good Idea of Demeter ! ! ! if !address.street.nil? || !address.street.empty?! string << address.street! end
44. The Pretty Good Idea of Demeter ! ! ! if !address.street.nil? || !address.street.empty?! string << address.street! end
45. The Pretty Good Idea of Demeter ! ! ! if !address.street.nil? || !address.street.empty?! string << address.street! end
46. The Pretty Good Idea of Demeter ! ! ! if !address.street.nil? || !address.street.empty?! string << address.street! end
47. my_television.front_panel.switches.power.on();
48. my_television.front_panel.switches.power.on();
49. my_television.front_panel.switches.power.on();
50. my_television.front_panel.switches.power.on();
51. my_television.front_panel.switches.power.on();
52. my_television.front_panel.switches.power.on();
53. my_television.front_panel.switches.power.on();
54. my_television.front_panel.switches.power.on();
55. my_television.front_panel.switches.power.on();
56. my_television.front_panel.switches.power.on();
57. my_television.front_panel.switches.power.on();
58. class User
    def watch_tv
    my_television.front_panel.switches.power.on
    end
    end
59. my_television.power_up();
60. class Person! def display_address! "".tap do |string|! if !address.street.nil? || !address.street.empty?! string << address.street! end! ! string << "\n" unless string.empty?! ! if !address.city.nil? address.city.empty? || address.city.nil?! string << address.city! end! ! if address.province || address.postal_code! string << ", "! end! ! if address.province || address.postal_code! if address.province! string << address.province! end! ! string << " "! !
61. class Person! def display_address! address.display! ! self! end! end!
62. class Person! def display_address! address.display! ! ! self! end! end! ! class Address! def display! "".tap do |string|! if !street.nil? || !street.empty?! string << street! end! ! string << "\n" unless string.empty?! ! if !city.nil? city.empty? || city.nil?! string << city! end! ! if province || postal_code! string << ", "! end!
63. RULE 2 OBJECTS MAY QUERY
 THEMSELVES
64. class Person! def display_address! address.display! ! ! self! end! end! ! class Address! def display! "".tap do |string|! if !street.nil? || !street.empty?! string << street! end! ! string << "\n" unless string.empty?! ! if !city.nil? city.empty? || city.nil?! string << city! end! ! if province || postal_code! string << ", "! end! RULE 2
65. class Address! def display! ! ! ! ! ! ! ! end! end
66. class Address! def display! province_and_postal_code = [province, postal_code].compact.join(' ')! province_and_postal_code = nil if province_and_postal_code.empty?! ! ! ! ! ! end! end "" "VA 22222" "VA 22222” "VA"
67. class Address! def display! province_and_postal_code = [province, postal_code].compact.join(' ')! province_and_postal_code = nil if province_and_postal_code.empty?! ! city_province_postal_code = [city, province_and_postal_code].compact.join(', ')! city_province_postal_code = nil if city_province_postal_code.empty?! ! ! end! end "Arlington" "VA 22222" “Arlington, VA 22222” “Arlington, VA"
68. class Address! def display! province_and_postal_code = [province, postal_code].compact.join(' ')! province_and_postal_code = nil if province_and_postal_code.empty?! ! city_province_postal_code = [city, province_and_postal_code].compact.join(', ')! city_province_postal_code = nil if city_province_postal_code.empty?! ! [street, city_province_postal_code].compact.join("\n")! end! end “123 Main St. Arlington” “123 Main St. VA 22222" “123 Main St. Arlington, VA 22222” “Arlington, VA"
69. class Address! def display! province_and_postal_code = [province, postal_code].compact.join(' ')! province_and_postal_code = nil if province_and_postal_code.empty?! ! city_province_postal_code = [city, province_and_postal_code].compact.join(', ')! city_province_postal_code = nil if city_province_postal_code.empty?! ! [street, city_province_postal_code].compact.join("\n")! end! end
70. class Address! def display(line_break="\n")! province_and_postal_code = [province, postal_code].compact.join(' ')! province_and_postal_code = nil if province_and_postal_code.empty?! ! city_province_postal_code = [city, province_and_postal_code].compact.join(', ')! city_province_postal_code = nil if city_province_postal_code.empty?! ! [street, city_province_postal_code].compact.join(line_break)! end! end
71. class Address! def display(line_break="\n")! province_and_postal_code = [province, postal_code].compact.join(' ')! province_and_postal_code = nil if province_and_postal_code.empty?! ! city_province_postal_code = [city, province_and_postal_code].compact.join(', ')! city_province_postal_code = nil if city_province_postal_code.empty?! ! [street, city_province_postal_code].compact.join(line_break)! end! end! ! class Person! def display_address(line_break)! address.display(line_break)! self! end! end
72. class Address! def display(line_break="\n")! province_and_postal_code = [province, postal_code].compact.join(' ')! province_and_postal_code = nil if province_and_postal_code.empty?! ! city_province_postal_code = [city, province_and_postal_code].compact.join(', ')! city_province_postal_code = nil if city_province_postal_code.empty?! ! [street, city_province_postal_code].compact.join(line_break)! end! end! ! class Person! def display_address(line_break)! address.display(line_break)! self! end! end
73. class Template! def display_address(address)! province_and_postal_code = [address.province, address.postal_code].compact.join(' ' province_and_postal_code = nil if province_and_postal_code.empty?! ! city_province_postal_code = [address.city, province_and_postal_code].compact.join(' city_province_postal_code = nil if city_province_postal_code.empty?! ! STDOUT.puts [address.street, city_province_postal_code].compact.join(“\n")! ! self! end! end
74. class Template! def display_address(address)! province_and_postal_code = [address.province, address.postal_code].compact.join(' ' province_and_postal_code = nil if province_and_postal_code.empty?! ! city_province_postal_code = [address.city, province_and_postal_code].compact.join(' city_province_postal_code = nil if city_province_postal_code.empty?! ! STDOUT.puts [address.street, city_province_postal_code].compact.join(“\n")! ! self! end! end! ! class HtmlTemplate! def display_address(address)! ! ! # data processing… ! ! File.open ‘address.html’ do |file|! file.write [address.street, city_province_postal_code].compact.join("<br />”)! end! ! self! end!
75. class Person! def display_address(template=Template.new)! address.display(template)! self! end! end
76. RULE 3 FACTORIES ARE EXEMPT
77. class Person! def display_address(template=Template.new)! address.display(template)! self! end! end RULE 3
78. class Person! def display_address(template=Template.new)! address.display(template)! self! end! end! ! class Address! def display(template)! template.display_address(self)! self! end! end!
79. class Person! def display_address(template=Template.new)! address.display(template)! self! end! end! ! class Address! def display(template)! template.display_address(self)! self! end! end! ! class Template! def display_address(address)! # data processing…! ! ! STDOUT.puts [address.street, city_province_postal_code].compact.join(“\n")! ! self! end! end
80. class Person! def display_address(template=Template.new)! address.display(template)! self! end! end! ! class Address! def display(template)! template.display_address(self)! self! end! end
81. class Person! def display_address(template=Template.new)! address.display(template)! self! end! end! ! ! ! ! class Address! def display(template)! template.display_address(self)! self! end! end
82. class Person! def display_address(template=Template.new)! address.display(template)! self! end! ! private! attr_reader :address! end! ! class Address! def display(template)! template.display_address(self)! self! end! ! private! attr_reader :street, :city, :province, :postal_code! end
83. class Address! def display(template)! template.display_address(self)! self! end! ! private! attr_reader :street, :city, :province, :postal_code! end
84. class Address! def display(template)! template.display_address(self)! self! end! ! private! attr_reader :street, :city, :province, :postal_code! end! ! class Template! def display_address(address)! province_and_postal_code = [address.province, address.postal_code].compact.join(' ' province_and_postal_code = nil if province_and_postal_code.empty?! ! city_province_postal_code = [address.city, province_and_postal_code].compact.join(' city_province_postal_code = nil if city_province_postal_code.empty?! ! STDOUT.puts [address.street, city_province_postal_code].compact.join(“\n")! ! self! end! end
85. class Address! def display(template)! template.display_address(self)! self! end! ! private! attr_reader :street, :city, :province, :postal_code! end! ! ! ! ! ! ! class Template! def display_address(address)! # …code…! end! end
86. class Address! def display(template)! template.display_address(to_value)! self! end! ! private! attr_reader :street, :city, :province, :postal_code! ! require ‘ostruct’! def to_value! OpenStruct.new(street: street, city: city, province: province, postal_code: postal_ end! end! ! class Template! def display_address(address)! # …code…! end! end
87. class Address! def display(template)! template.display_address(to_value)! self! end! ! private! attr_reader :street, :city, :province, :postal_code! ! require ‘ostruct’! def to_value! OpenStruct.new(street: street, city: city, province: province, postal_code: postal_ end! end! ! class Template! def display_address(address)! # …code…! end! end
88. “123 Main St. Arlington” “123 Main St. VA 22222" “123 Main St. Arlington, VA 22222” “Arlington, VA"
89. class Address! def display(template)! template.display_address(to_value)! self! end! ! private! attr_reader :street, :city, :province, :postal_code! ! require ‘ostruct’! def to_value! OpenStruct.new(street: street, city: city, province: province, postal_code: postal_ end! end
90. class Address! def display(template)! template.display_address(to_value)! self! end! ! private! attr_reader :street, :city, :province, :postal_code! ! require ‘ostruct’! def to_value! if protect_privacy?! OpenStruct.new(street: nil, city: city, province: province, postal_code: nil)! else! OpenStruct.new(street: street, city: city, province: province, postal_code: posta end! end! end
91. class Template! def display_address(address)! province_and_postal_code = [address.province, address.postal_code].compact.join(' ' province_and_postal_code = nil if province_and_postal_code.empty?! ! city_province_postal_code = [address.city, province_and_postal_code].compact.join(' city_province_postal_code = nil if city_province_postal_code.empty?! ! STDOUT.puts [address.street, city_province_postal_code].compact.join(“\n")! ! self! end! end
92. class Template! def display_address(address)! province_and_postal_code = [address.province, address.postal_code].compact.join(' ' province_and_postal_code = nil if province_and_postal_code.empty?! ! city_province_postal_code = [address.city, province_and_postal_code].compact.join(' city_province_postal_code = nil if city_province_postal_code.empty?! ! STDOUT.puts [address.street, city_province_postal_code].compact.join(“\n")! ! self! end! end QUERIES EVERYWHERE
93. RULE 4 BREAK
 THE RULES SPARINGLY
94. class Person! def display_address(template=Template.new)! address.display(template)! self! end! end! ! class Address! def display(template)! template.display_address(self)! self! end! end! ! class Template! def display_address(address)! # data processing…! ! ! STDOUT.puts […].compact.join(“\n”)! ! self! end! end
95. EAST ORIENTED James Ladd
96. EAST ORIENTED James Ladd The structuring of code to an 
 East orientation decreases coupling and the amount of code needed to be written, whilst increasing code clarity, cohesion and flexibility.
97. EAST ORIENTED James Ladd The structuring of code to an 
 East orientation decreases coupling and the amount of code needed to be written, whilst increasing code clarity, cohesion and flexibility.
98. COMMANDS QUERIES
99. LEAK
100. LEAK KNOWLEDGE
101. LEAK RESPONSIBILITY
102. POLYMORPHISM
103. ENCAPSULATION
104. LOOSEN COUPLING
105. IDEMPOTENT
106. EAST ORIENTED
107. RULE 1 ALWAYS RETURN SELF
108. RULE 2 OBJECTS MAY QUERY THEMSELVES
109. RULE 3 FACTORIES ARE EXEMPT
110. RULE 4 BREAK
 THE RULES SPARINGLY
111. TELL JAMES
     THANKS @jamesladd The East principle 
 is not like the 
 “Tell, Don’t Ask” principle because there is no ambiguity, you simply cannot ask, you can only tell.
112. TELL JAMES
     THANKS @jamesladd The East principle 
 is not like the 
 “Tell, Don’t Ask” principle because there is no ambiguity, you simply cannot ask, you can only tell.
113. What if we had tools to help guide us?
114. Let’s try it
115. class Person! ! ! attr_reader :friend! end! ! class Friend! def make_me_a_sandwich! Table.place "a sandwich!"! end! end!
116. class Person! ! ! attr_reader :friend! ! def make_me_a_sandwich! friend.make_me_a_sandwich! end! end! ! class Friend! def make_me_a_sandwich! Table.place "a sandwich!"! end! end
117. class Person! extend Forwardable! delegate :make_me_a_sandwich => :friend! attr_reader :friend! end! ! class Friend! def make_me_a_sandwich! Table.place "a sandwich!"! end! end!
118. gem install
     direction
119. describe Direction do! let(:friend){ Friend.new }! let(:person){ person = Person.new! person.friend = friend! person! }! before do! Table.clear! end! it 'forwards a message to another object' do! assert_equal [], Table.contents! person.make_me_a_sandwich! assert_includes Table.contents, "a sandwich!"! end! end
120. describe Direction do! let(:friend){ Friend.new }! let(:person){ person = Person.new! person.friend = friend! person! }! before do! Table.clear! end! it 'forwards a message to another object' do! assert_equal [], Table.contents! person.friend.make_me_a_sandwich! assert_includes Table.contents, "a sandwich!"! end! ! ! !
121. class Person! extend Forwardable! delegate :make_me_a_sandwich => :friend! attr_reader :friend! end! ! class Friend! def make_me_a_sandwich! Table.place "a sandwich!"! end! end!
122. class Person! extend Forwardable! delegate :make_me_a_sandwich => :friend! ! private! attr_reader :friend! end! ! class Friend! def make_me_a_sandwich! Table.place "a sandwich!"! end! end!
123. class Person! extend Direction! command :make_me_a_sandwich => :friend! ! private! attr_accessor :friend! end! ! class Friend! def make_me_a_sandwich! Table.place "a sandwich!"! end! end!
124. describe Direction do! let(:friend){ Friend.new }! let(:person){ person = Person.new! person.friend = friend! person! }! before do! Table.clear! end! it 'forwards a message to another object' do! assert_equal [], Table.contents! person.make_me_a_sandwich! assert_includes Table.contents, "a sandwich!"! end! ! it 'returns the original receiver' do! assert_equal person, person.make_me_a_sandwich! end!
125. describe Direction do! ! it 'returns the original receiver' do! assert_equal person, person.make_me_a_sandwich! end! end
126. describe Direction do! ! it 'returns the original receiver' do! assert_equal person, person.make_me_a_sandwich.
     ! ! get_me_a_drink! end! end
127. describe Direction do
     ! it 'returns the original receiver' do! assert_equal person, person.make_me_a_sandwich.
     ! ! get_me_a_drink.
     ! ! wash_the_car! end! end
128. describe Direction do! ! it 'returns the original receiver' do! assert_equal person, person.make_me_a_sandwich.
     ! ! get_me_a_drink.
     ! ! wash_the_car.
     ! ! jump! end! end
129. describe Direction do! ! it 'returns the original receiver' do! assert_equal person, person.make_me_a_sandwich.
     ! ! get_me_a_drink.
     ! ! wash_the_car.
     ! ! jump.
     ! ! gimme_five! end! end
130. describe Direction do! ! it 'returns the original receiver' do! assert_equal person, person.make_me_a_sandwich.
     ! ! get_me_a_drink.
     ! ! wash_the_car.
     ! ! jump.
     ! ! gimme_five.
     ! ! up_high! end! end
131. describe Direction do! ! it 'returns the original receiver' do! assert_equal person, person.make_me_a_sandwich.
     ! ! get_me_a_drink.
     ! ! wash_the_car.
     ! ! jump.
     ! ! gimme_five.
     ! ! up_high.
     ! ! down_low! end! end
132. describe Direction do! ! it 'returns the original receiver' do! assert_equal person, person.make_me_a_sandwich.
     ! ! get_me_a_drink.
     ! ! wash_the_car.
     ! ! jump.
     ! ! gimme_five.
     ! ! up_high.
     ! ! down_low.
     ! ! too_slow! end! end
133. module Direction! def command(options)! method_defs = []! options.each_pair do |key, value|! Array(key).map do |command_name|! method_defs.unshift %{! def #{command_name}(*args, &block)! #{value}.__send__(:#{command_name}, *args, &block)! self! end! }! end! end! self.class_eval method_defs.join(' ')! end! end
134. module Direction! def command(options)! method_defs = []! options.each_pair do |key, value|! Array(key).map do |command_name|! method_defs.unshift %{! def #{command_name}(*args, &block)! #{value}.__send__(:#{command_name}, *args, &block)! self! end! }! end! end! self.class_eval method_defs.join(' ')! end! end
135. class Person! extend Direction! command [:make_me_a_sandwich, :other] => :friend! ! private! attr_accessor :friend! end! ! class Friend! def make_me_a_sandwich! Table.place "a sandwich!"! end! end!
136. CHANGE YOUR CODE
137. RETURN SELF
138. RUN YOUR TESTS
139. DID IT BREAK?
140. IT’S TELLING YOU SOMETHING
141. GO EAST
142. THANK
     YOU
143. THANK
     YOU clean-ruby.com
144. BUY THE BOOK clean-ruby.com
145. BUY THE BOOK clean-ruby.com RC2EC
     25% off