The Case of the Missing Method — A Ruby Mystery Story

Business is slow for Ruby Private Investigator, Deirdre Bug. She’s on the verge of switching industry when she gets a call from an anxious young man. "Some class methods have gone missing," he tells her breathlessly. "I need your help."

Deirdre takes the case and begins exploring Ruby objects behind the scenes. Though she thinks she's on familiar ground — Ruby's object model, method lookup — she's about to discover that she really has no clue.

Transcript

1. THE CASE OF THE MISSING METHOD A Ruby Mystery Story Nadia Odunayo, @nodunayo
2. Side hustle?
4. "
7. Nadia Odunayo
8. Nadia Odunayo
9. Deirdre Bug
10. Deirdre Bug
11. Dee Bug
12. CASE FILES #017 Missing Method
13. CHAPTER ONE
14. "
15. $
16. Mike • 24 years old • Junior Ruby developer • TDD-enthusiast %
17. Apprenticeship Ruby Institute of Professionals (RIP)
18. Jenny • 27 years old • Junior Ruby developer • Rails worshipper & • Mike’s best friend
19. ' & “May the best person win!”
20. Method lookup &
21. $ Something doesn’t add up in Jenny’s notes!
22. &
23. $ You can help me find the answer!
26. class
27. instance object class
28. instance object class class object
29. instance object class class object class methods method_one method_two method_three
30. & Any class you define is an instance of a class object called ‘Class'
31. class Cake is an instance of class Class
32. class Cake … def tasty? @flavour == “carrot” end def self.edible? true end end
33. carrot = Cake.new
34. carrot class Cake class methods tasty? def tasty? @flavour == “carrot” end Class methods edible? def edible? true end
35. & A method definition always comes from an object's class!
36. carrot class Cake class methods tasty? def tasty? @flavour == “carrot” end Class methods edible? def edible? true end
37. class Cake … def tasty? @flavour == “carrot” end def self.edible? true end end
39. +
40. "
42. ,
43. CHAPTER TWO
46. " The ‘edible?’ method must be somewhere in the ancestry tree!
48. def where?(object, method) object.class.ancestors.detect { | klass | klass.instance_methods(false).include?(method) } end
49. def where?(object, method) object.class.ancestors.detect { | klass | klass.instance_methods(false).include?(method) } end
50. def where?(object, method) object.class.ancestors.detect { | klass | klass.instance_methods(false).include?(method) } end
51. def where?(object, method) object.class.ancestors.detect { | klass | klass.instance_methods(false).include?(method) } end
52. def where?(object, method) object.class.ancestors.detect { | klass | klass.instance_methods(false).include?(method) } end
53. def where?(object, method) object.class.ancestors.detect { | klass | klass.instance_methods(false).include?(method) } end
55. +
56. "
57. /01 234 567
58. $ ObjectSpace
59. 8 You can interact with all the ‘live’ objects within a Ruby session!
60. ObjectSpace.count_objects[:T_CLASS]
62. +
63. Where are you?!
64. :
65. CHAPTER THREE
66. A Little Chat about Smalltalk A Lecture by Adele Alan ;
67. Smalltalk Born 1970 Adele Alan ;
68. Smalltalk The birth of object-oriented programming Adele Alan ;
69. "
70. " One class, yet two objects?!
71. …psst! Pay attention!!
72. What is the ‘class of a class’ in Smalltalk? ;
73. Adele Alan ;
74. Adele Alan ;
75. The ‘class of a class’ is called a metaclass. ;
76. Smalltalk Adele Alan Objective-C ;
77. Smalltalk Adele Alan Objective-C Java ;
78. Smalltalk Adele Alan Objective-C Java Python ;
79. Smalltalk Adele Alan Objective-C Java Ruby Python ;
80. =
82. def where?(object, method) object.class.ancestors.detect { | klass | klass.instance_methods(false).include?(method) } end
83. def where?(object, method) object.singleton_class.ancestors.detect { | klass | klass.instance_methods(false).include?(method) } end
85. CHAPTER FOUR
87. "Can I come round?! ' Of course!!
88. "
89. Singleton classes?
91. A Ellen • 43 years old • Freelance developer • Ruby committer
92. "
93. " Singleton classes — what are they?
94. A Internal classes to hold methods defined for one particular object.
95. " When does knowing about them become useful?
96. Budgeting Inc. Personal finance for small business owners
97. Budgeting Inc. A The codebase was a mess! •Lots of duplicate code •Inefficient development •Bugs and oversights
98. / 0 1 ☹
99. D ☹
100. A I decided to create a DSL — a Domain Specific Language.
101. +
102. A Let me show you a basic version of a DSL…
103. class CityInstance def self.construct(&block) city = new city.instance_eval(&block)
 city end 
 attr_reader :taxes 
 
 def initialize
 @taxes = []
 end
 
 def tax(name)
 @taxes.push(name)
 end end

104. class CityInstance def self.construct(&block) city = new city.instance_eval(&block)
 city end 
 attr_reader :taxes 
 
 def initialize
 @taxes = []
 end
 
 def tax(name)
 @taxes.push(name)
 end end

105. class CityInstance def self.construct(&block) city = new city.instance_eval(&block)
 city end 
 attr_reader :taxes 
 
 def initialize
 @taxes = []
 end
 
 def tax(name)
 @taxes.push(name)
 end end

106. class CityInstance def self.construct(&block) city = new city.instance_eval(&block)
 city end 
 attr_reader :taxes 
 
 def initialize
 @taxes = []
 end
 
 def tax(name)
 @taxes.push(name)
 end end

107. class CityInstance def self.construct(&block) city = new city.instance_eval(&block)
 city end 
 attr_reader :taxes 
 
 def initialize
 @taxes = []
 end
 
 def tax(name)
 @taxes.push(name)
 end end

108. class CityInstance def self.construct(&block) city = new city.instance_eval(&block)
 city end 
 attr_reader :taxes 
 
 def initialize
 @taxes = []
 end
 
 def tax(name)
 @taxes.push(name)
 end end

109. class CityInstance def self.construct(&block) city = new city.instance_eval(&block)
 city end 
 attr_reader :taxes 
 
 def initialize
 @taxes = []
 end
 
 def tax(name)
 @taxes.push(name)
 end end

110. class CityInstance def self.construct(&block) city = new city.instance_eval(&block)
 city end 
 attr_reader :taxes 
 
 def initialize
 @taxes = []
 end
 
 def tax(name)
 @taxes.push(name)
 end end

111. class CityInstance def self.construct(&block) city = new city.instance_eval(&block)
 city end 
 attr_reader :taxes 
 
 def initialize
 @taxes = []
 end
 
 def tax(name)
 @taxes.push(name)
 end end

112. class CityInstance def self.construct(&block) city = new city.instance_eval(&block)
 city end 
 attr_reader :taxes 
 
 def initialize
 @taxes = []
 end
 
 def tax(name)
 @taxes.push(name)
 end end

114. A The DSL allowed for quick and easy scaffolding of each new City subclass and any related classes.
116. Budgeting Inc. A • Effortless scaffolding • Better maintainability • Easier customisation All common code was consolidated in one place!
117. / 0 1
118. D
120. A Grasping singleton classes can save you from a lot of headache.
121. A But, beware…!
122. To DSL? •Complex repeated business rules? •Need to customise behaviour in some specific instances? ,
123. A Using Rails? You see DSLs every single day.
126. A Rails magic?
127. A Rails magic? A collection of well-written DSLs.
129. A Complex Rails or Ruby? Funny bug? Singleton classes, perhaps…!
130. F
131. G
133. carrot class Cake class methods tasty? def tasty? @flavour == “carrot” end Cake singleton methods edible? def edible? true end
134. G Jenny knew about singleton classes all along…
135. &
136. "
137. G My best friend tried to sabotage me!
138. " You can’t give up now!!
139. " Have you heard of DSLs…?
140. G
141. EPILOGUE 2 months later…
142. Hack Night
143. Oooh..! She’s Ruby famous…!
144. A
145. " Singleton classes — do I have to care about them?
146. A Not really…
147. Simplicity
148. Consistency
149. A Every method in Ruby is an instance method.
150. Invisible Yet Everywhere
151. "
152. " Ruby Private Investigator Specialising in Ruby internals…? Deirdre Bug
153. EPILOGUE Again
154. Due to being distraught at Jenny’s betrayal, Mike performed badly at the RIP interview… ジェニーの裏切りに動揺した結果、 マイクはRIPの⾯面接に失敗してしま う。
155. Jenny is 3 months into an apprenticeship at the RIP. ジェニーはRIP社にて３ヶ⽉月⽬目の⾒見見習い 中。
156. Mike and Jenny no longer speak. マイクとジェニーはもう⼝口もきかない関係となっ た。
157. Mike is still looking for work. マイクはいまだ求職中である。
158. The shady mastermind behind Ruby is still at large… Rubyを陰で操る黒幕は今だ不不明である。
159. THE END? 終 ?
160. SOURCES FRIENDS OF DEE Ruby Under A Microscope Book by Pat Shaughnessy
 Ruby, Smalltalk and Class Variables Blog post by Pat Shaughnessy
 Ruby Tapas — Episodes 453, 454, and 456 Screencasts by Avdi Grimm Benefits of Writinng a DSL in Ruby Blog post by Gusto
 DslQandA Blog post by Martin Fowler Eigen What Now? Talk by Eliza de Jager Aaron Patterson Adam Cuppy Aly Blenkin Andy Croll Ana Carlos Avdi Grimm Ebi Jonathan Tsang Pat Shaughnessy Saron Yitbarek Tammer Saleh Nadia Odunayo, @nodunayo