Metaprogramming? Not good enough!

If you know how to metaprogram in Ruby, you can create methods and objects on the fly, build Domain Specific Languages, or just save yourself a lot of typing. But can you change how methods are dispatched? Can you decide that the normal inheritance rules don't apply to some object?

In order to change those core parts of the language, there can't be much difference between how a language is implemented and how it's used. In this talk, you'll make that difference smaller, building a totally extensible object model on top of Ruby, using less than a dozen new classes and methods.

Transcript

1. Metaprogramming? Not good enough! Justin Weiss @justinweiss | #tinyobj
2. Metaprogramming? Not good enough! Justin Weiss @justinweiss | #tinyobj
3. @justinweiss | #tinyobj
4. @justinweiss | #tinyobj
5. @justinweiss | #tinyobj
6. @justinweiss | #tinyobj
7. → 2005: Ruby @justinweiss | #tinyobj
8. → 2005: Ruby → 2006: JavaScript Ruby @justinweiss | #tinyobj
9. → 2005: Ruby → 2006: JavaScript Ruby → 2007: Erlang Ruby @justinweiss | #tinyobj
10. → 2005: Ruby → 2006: JavaScript Ruby → 2007: Erlang Ruby → ... → 2015: Swift Ruby @justinweiss | #tinyobj
11. What makes Ruby, Ruby? @justinweiss | #tinyobj
12. @justinweiss | #tinyobj
13. Erlang = Actors @justinweiss | #tinyobj
14. Erlang = Actors Haskell = Monads @justinweiss | #tinyobj
15. Erlang = Actors Haskell = Monads Lisp = Parentheses @justinweiss | #tinyobj
16. Erlang = Actors Haskell = Monads Lisp = Parentheses Macros @justinweiss | #tinyobj
17. Erlang = Actors Haskell = Monads Lisp = Parentheses Macros Ruby = Metaprogramming? @justinweiss | #tinyobj
18. @justinweiss | #tinyobj
19. Metaprogramming → !? @justinweiss | #tinyobj
20. @justinweiss | #tinyobj
21. @justinweiss | #tinyobj
22. @justinweiss | #tinyobj
23. @justinweiss | #tinyobj
24. @justinweiss | #tinyobj
25. A brand new object model (on top of Ruby) @justinweiss | #tinyobj
26. Object model The concepts, data structures, and methods you use to build things in your language @justinweiss | #tinyobj
27. @justinweiss | #tinyobj
28. I. Piumarta and A. Warth Open, Extensible Object Models http://piumarta.com/software/cola/ objmodel2.pdf @justinweiss | #tinyobj
29. When you have a method name and arguments, which code do you use? @justinweiss | #tinyobj
30. When you have a method name and arguments, which code do you use? @justinweiss | #tinyobj
31. def lookup(object, method_name) # Look up a method by name in object's methods list # If it exists, return it # Otherwise, if you have a parent class, recurse end @justinweiss | #tinyobj
32. @justinweiss | #tinyobj
33. @justinweiss | #tinyobj
34. What is behavior? @justinweiss | #tinyobj
35. @justinweiss | #tinyobj
36. @justinweiss | #tinyobj
37. @justinweiss | #tinyobj
38. @justinweiss | #tinyobj
39. @justinweiss | #tinyobj
40. @justinweiss | #tinyobj
41. @justinweiss | #tinyobj
42. Object = a thing Class = a thing that builds objects, holds methods, has a parent Behavior = a thing that holds methods like lookup and add_method @justinweiss | #tinyobj
43. Object add_method lookup @justinweiss | #tinyobj
44. How do we get an object from a class? @justinweiss | #tinyobj
45. Object add_method lookup build_object @justinweiss | #tinyobj
46. What about new classes, sub-classes, or sub- behaviors? @justinweiss | #tinyobj
47. Object add_method lookup build_object delegate @justinweiss | #tinyobj
48. How do you call a method? @justinweiss | #tinyobj
49. Object add_method lookup build_object delegate send @justinweiss | #tinyobj
50. Let's build it in Ruby! @justinweiss | #tinyobj
51. class TinyObject < BasicObject attr_accessor :state attr_accessor :behavior end @justinweiss | #tinyobj
52. class TinyObject < BasicObject attr_accessor :state attr_accessor :behavior end @justinweiss | #tinyobj
53. Create the core methods @justinweiss | #tinyobj
54. behavior_add_method = lambda do |behavior, method_name, method| behavior.state[:methods][method_name] = method end @justinweiss | #tinyobj
55. behavior_add_method = lambda do |behavior, method_name, method| # -------^ behavior.state[:methods][method_name] = method end @justinweiss | #tinyobj
56. behavior_lookup = lambda do |behavior, method_name| # ... end @justinweiss | #tinyobj
57. behavior_lookup = lambda do |behavior, method_name| # Look up a method by name in the object's methods list method = behavior.state[:methods][method_name] # ... method end @justinweiss | #tinyobj
58. behavior_lookup = lambda do |behavior, method_name| # ... # If you can't find it, but have a parent class... if !method && behavior.state[:parent] # call this method recursively, using the parent instead method = behavior_lookup.call(behavior.state[:parent], method_name) end method end @justinweiss | #tinyobj
59. behavior_lookup = lambda do |behavior, method_name| # Look up a method by name in the object's methods list method = behavior.state[:methods][method_name] # If you can't find it, but have a parent class... if !method && behavior.state[:parent] # call this method recursively, using the parent instead method = behavior_lookup.call(behavior.state[:parent], method_name) end method end @justinweiss | #tinyobj
60. behavior_build_object = lambda do |behavior| # Allocate an object obj = TinyObject.new obj.state = {} # set the object's class / behavior # to yourself (the class that called this method) obj.behavior = behavior # return the object obj end @justinweiss | #tinyobj
61. behavior_delegate = lambda do |parent_class| # ... end @justinweiss | #tinyobj
62. @justinweiss | #tinyobj
63. subclass = behavior_build_object.call(parent_class.behavior) @justinweiss | #tinyobj
64. # set the object's parent (in its state) to ourselves subclass.state[:parent] = parent_class # initialize the object's state with an empty set of methods subclass.state[:methods] ||= {} subclass @justinweiss | #tinyobj
65. behavior_delegate = lambda do |parent_class| parent_class_behavior = parent_class && parent_class.behavior subclass = behavior_build_object.call(parent_class_behavior) # set the object's parent (in its state) to ourselves subclass.state[:parent] = parent_class # initialize the object's state with an empty set of methods subclass.state[:methods] ||= {} subclass end @justinweiss | #tinyobj
66. TinyObject: Our object structure, containing behavior and state behavior_add_method: Add a method to a class behavior_lookup: Find an implementation, from a method name behavior_build_object: Like .new, build an object from a class / behavior behavior_delegate: Inherit from a class / behavior @justinweiss | #tinyobj
67. @justinweiss | #tinyobj
68. default_behavior = behavior_delegate.call(nil) # ... @justinweiss | #tinyobj
69. default_behavior = behavior_delegate.call(nil) default_behavior.behavior = default_behavior @justinweiss | #tinyobj
70. root_object_class = behavior_delegate.call(nil) root_object_class.behavior = default_behavior @justinweiss | #tinyobj
71. root_object_class = behavior_delegate.call(nil) root_object_class.behavior = default_behavior @justinweiss | #tinyobj
72. # ... default_behavior.state[:parent] = root_object_class @justinweiss | #tinyobj
73. default_behavior = behavior_delegate.call(nil) default_behavior.behavior = default_behavior root_object_class = behavior_delegate.call(nil) root_object_class.behavior = default_behavior default_behavior.state[:parent] = root_object_class @justinweiss | #tinyobj
74. behavior_add_method.call(default_behavior, "lookup", behavior_lookup) behavior_add_method.call(default_behavior, "add_method", behavior_add_method) behavior_add_method.call(default_behavior, "build_object", behavior_build_object) behavior_add_method.call(default_behavior, "delegate", behavior_delegate) @justinweiss | #tinyobj
75. @justinweiss | #tinyobj
76. @justinweiss | #tinyobj
77. object_send = lambda do |object, method_name, *args| method = find_method.call(object, method_name) if method method.call(object, *args) else raise "No method #{method_name} found on object" end end @justinweiss | #tinyobj
78. find_method = lambda do |object, method_name| object_send.call(object.behavior, "lookup", method_name) end @justinweiss | #tinyobj
79. find_method = lambda do |object, method_name| if (object == default_behavior && method_name == "lookup") behavior_lookup.call(default_behavior, "lookup") else object_send.call(object.behavior, "lookup", method_name) end end @justinweiss | #tinyobj
80. behavior_add_method: Add a method to a class behavior_lookup: Find an implementation, from a method name behavior_build_object: Like .new, build an object from a class / behavior behavior_delegate: Inherit from a class / behavior object_send: Call a method, by name, on an object @justinweiss | #tinyobj
81. greeter_class = object_send.call(root_object_class, "delegate") @justinweiss | #tinyobj
82. greeter_class = object_send.call(root_object_class, "delegate") object_send.call(greeter_class, "add_method", "hello", lambda { |object| puts "Hello, world!" }) @justinweiss | #tinyobj
83. greeter = object_send.call(greeter_class, "build_object") object_send.call(greeter, "hello") # => @justinweiss | #tinyobj
84. greeter = object_send.call(greeter_class, "build_object") object_send.call(greeter, "hello") # => "Hello, world!" @justinweiss | #tinyobj
85. @justinweiss | #tinyobj
86. greeter = object_send.call(greeter_class, "build_object") object_send.call(greeter, "hello") # => "Hello, world!" @justinweiss | #tinyobj
87. @justinweiss | #tinyobj
88. class TinyObject < BasicObject attr_accessor :state attr_accessor :behavior def method_missing(name, *args) object_send = nil behavior = self.behavior # Crawl our ancestors for an "object_send" implementation while !object_send && behavior object_send = behavior.state[:methods]["object_send"] behavior = behavior.state[:parent] end # Call object_send on ourselves object_send.call(self, name.to_s, *args) end end @justinweiss | #tinyobj
89. object_send.call(greeter, "hello") @justinweiss | #tinyobj
90. object_send.call(greeter, "hello") ⬇ greeter.hello @justinweiss | #tinyobj
91. behavior_add_method.call(root_object_class, "object_send", object_send) @justinweiss | #tinyobj
92. greeter_class.add_method("hello_name", lambda { |object| puts "Hello, #{object.state[:name]}!" }) # ----^ @justinweiss | #tinyobj
93. alice = greeter_class.build_object bob = greeter_class.build_object alice.state[:name] = "Alice" bob.state[:name] = "Bob" alice.hello_name # => bob.hello_name # => @justinweiss | #tinyobj
94. alice = greeter_class.build_object bob = greeter_class.build_object alice.state[:name] = "Alice" bob.state[:name] = "Bob" alice.hello_name # => "Hello, Alice!" bob.hello_name # => "Hello, Bob!" @justinweiss | #tinyobj
95. Now what? @justinweiss | #tinyobj
96. Log method calls! @justinweiss | #tinyobj
97. def lookup # Get the old lookup method from the parent of our behavior # Call it to find the real method implementation # Wrap the method and return it end @justinweiss | #tinyobj
98. method_logger = lambda do |method_name, method, *args| puts "> Calling #{method_name}... " method.call(*args) puts "> Done!" end @justinweiss | #tinyobj
99. @justinweiss | #tinyobj
100. intercepting_behavior = default_behavior.delegate @justinweiss | #tinyobj
101. intercepting_behavior.add_method( "lookup", lambda do |sender, method_name| # Get the old lookup method from the parent of our class's behavior lookup = object_send.call(sender.behavior.state[:parent], "lookup", "lookup") # Call it to find the real method implementation method = lookup.call(sender, method_name) # Wrap the method and return it if method original_method = method interceptor = sender.state[:interceptor_method] method = lambda { |*args| interceptor.call(method_name, original_method, *args) } end method end ) @justinweiss | #tinyobj
102. # Get the old lookup method # from the parent of our class's behavior super_behavior = ? lookup = super_behavior.lookup("lookup") @justinweiss | #tinyobj
103. super_behavior = sender.behavior.state[:parent] lookup = super_behavior.lookup("lookup") @justinweiss | #tinyobj
104. # Get the old lookup method # from the parent of our class's behavior super_behavior = sender.behavior.state[:parent] lookup = super_behavior.lookup("lookup") # Call lookup to find the real method implementation method = lookup.call(sender, method_name) @justinweiss | #tinyobj
105. # Wrap the method and return it if method original_method = method interceptor = sender.state[:interceptor_method] method = lambda do |*args| interceptor.call(method_name, original_method, *args) end end method @justinweiss | #tinyobj
106. @justinweiss | #tinyobj
107. person_class = root_object_class.delegate # ... @justinweiss | #tinyobj
108. person_class = root_object_class.delegate person_class.behavior = intercepting_behavior @justinweiss | #tinyobj
109. person_class = root_object_class.delegate # ... @justinweiss | #tinyobj
110. person_class = root_object_class.delegate person_class.behavior = intercepting_behavior @justinweiss | #tinyobj
111. method_logger = lambda do |method_name, method, *args| puts "> Calling #{method_name}... " method.call(*args) puts "> Done!" end person_class.state[:interceptor_method] = method_logger @justinweiss | #tinyobj
112. person_class.add_method "name", lambda { |_| puts "Justin" } person_class.add_method "location", lambda { |_| puts "Cincinnati, OH" } @justinweiss | #tinyobj
113. person = person_class.build_object person.name # # # person.location # # # @justinweiss | #tinyobj
114. person = person_class.build_object person.name # > Calling name... # Justin # > Done! person.location # > Calling location... # Cincinnati, OH # > Done! @justinweiss | #tinyobj
115. @justinweiss | #tinyobj
116. person_class.behavior = default_behavior person.name # @justinweiss | #tinyobj
117. person_class.behavior = default_behavior person.name # Justin @justinweiss | #tinyobj
118. Retry method calls! @justinweiss | #tinyobj
119. person_class.add_method("flaky_method", lambda do |_| if rand(3) == 0 puts "Success!" true else false end end) @justinweiss | #tinyobj
120. retry_interceptor = lambda do |method_name, method, *args| until method.call(*args) puts "Method #{method_name} failed, retrying..." sleep 0.5 end end @justinweiss | #tinyobj
121. person_class.state[:interceptor_method] = retry_interceptor person.flaky_method @justinweiss | #tinyobj
122. person_class.state[:interceptor_method] = retry_interceptor person.flaky_method # Method flaky_method failed, retrying... @justinweiss | #tinyobj
123. person_class.state[:interceptor_method] = retry_interceptor person.flaky_method # Method flaky_method failed, retrying... # Method flaky_method failed, retrying... @justinweiss | #tinyobj
124. person_class.state[:interceptor_method] = retry_interceptor person.flaky_method # Method flaky_method failed, retrying... # Method flaky_method failed, retrying... # Method flaky_method failed, retrying... @justinweiss | #tinyobj
125. person_class.state[:interceptor_method] = retry_interceptor person.flaky_method # Method flaky_method failed, retrying... # Method flaky_method failed, retrying... # Method flaky_method failed, retrying... # Method flaky_method failed, retrying... @justinweiss | #tinyobj
126. person_class.state[:interceptor_method] = retry_interceptor person.flaky_method # Method flaky_method failed, retrying... # Method flaky_method failed, retrying... # Method flaky_method failed, retrying... # Method flaky_method failed, retrying... # Success! @justinweiss | #tinyobj
127. @justinweiss | #tinyobj
128. Multiple Inheritance @justinweiss | #tinyobj
129. @justinweiss | #tinyobj
130. @justinweiss | #tinyobj
131. @justinweiss | #tinyobj
132. @justinweiss | #tinyobj
133. multiple_parents_behavior = default_behavior.delegate @justinweiss | #tinyobj
134. multiple_parents_behavior.add_method("add_parent", lambda do |behavior, new_parent| # Initialize `parents` with the original parent unless behavior.state[:parents] behavior.state[:parents] = [] parent = behavior.state[:parent] behavior.state[:parents] << parent if parent end # Append the new parent to `parents` behavior.state[:parents] << new_parent end ) @justinweiss | #tinyobj
135. multiple_parents_behavior.add_method( "lookup", lambda do |behavior, method_name| method = behavior.state[:methods][method_name] parents = behavior.state[:parents] || [behavior.state[:parent]] if !method && parents parents.each do |parent| break if method = parent.lookup(method_name) end end method end ) @justinweiss | #tinyobj
136. multiple_parents_behavior.add_method( "lookup", lambda do |behavior, method_name| method = behavior.state[:methods][method_name] parents = behavior.state[:parents] || [behavior.state[:parent]] if !method && parents parents.each do |parent| # v---- -----^ break if method = parent.lookup(method_name) end end method end ) @justinweiss | #tinyobj
137. person_class = root_object_class.delegate person_class.add_method "name", lambda { |_| puts "Justin" } greeter_class = root_object_class.delegate greeter_class.add_method "greeting", lambda { |_| puts "Hello! Hello! Hello!" } @justinweiss | #tinyobj
138. social_person_class = person_class.delegate social_person_class.behavior = multiple_parents_behavior social_person_class.add_parent(greeter_class) @justinweiss | #tinyobj
139. justin = social_person_class.build_object justin.name # => justin.greeting # => @justinweiss | #tinyobj
140. justin = social_person_class.build_object justin.name # => "Justin" justin.greeting # => "Hello! Hello! Hello!" @justinweiss | #tinyobj
141. → Single inheritance → Interception → Multiple Inheritance @justinweiss | #tinyobj
142. → Object → add_method → lookup → build_object → delegate → send @justinweiss | #tinyobj
143. Modules? method_missing? BasicObject? delegation? @justinweiss | #tinyobj
144. Intent @justinweiss | #tinyobj
145. What's normal? @justinweiss | #tinyobj
146. @justinweiss | #tinyobj
147. @justinweiss | #tinyobj
148. What? Why!? @justinweiss | #tinyobj
149. @justinweiss | #tinyobj
150. The best way to understand a system is to break it. @justinweiss | #tinyobj
151. symbols.each do |symbol| klass = Class.new(ActiveRecord::Base) do def method_missing(name, *args) # ... end end Object.const_set(symbol.to_s.capitalize, klass) end @justinweiss | #tinyobj
152. @justinweiss | #tinyobj
153. @justinweiss | #tinyobj
154. Try it out @justinweiss | #tinyobj
155. Thank you! Justin Weiss @justinweiss https://www.avvo.com justin@justinweiss.com https://www.justinweiss.com/ rubyconf-2016 @justinweiss | #tinyobj
156. Thank you! Justin Weiss @justinweiss https://www.avvo.com justin@justinweiss.com https://www.justinweiss.com/ rubyconf-2016 @justinweiss | #tinyobj
157. The Ruby logo is Copyright © 2006, Yukihiro Matsumoto. It is licensed under the terms of the Creative Commons Attribution- ShareAlike 2.5 License agreement. "Happy Programmers" by Jesper Rønn-Jensen, used under CC BY- SA 2.0 / Resized from original "Laptop Stickers" by Nate Angell, used under CC BY 2.0 / Resized from original "No Brain" by Pierre-Olivier Carles, used under CC BY 2.0 @justinweiss | #tinyobj