Applying the Module Builder Pattern

Slides given on 2017-08-03 at Cleveland Ruby Brigade

A walkthrough of a refactor in Ruby illustrating how to apply the Module Builder pattern. Also introduces some basic metaprogramming techniques that are more widely-applicable.

Much appreciation to Chris Salzberg who coined the pattern and discusses it in-depth here: http://dejimata.com/2017/5/20/the-ruby-module-builder-pattern

Transcript

1. Applying the Module Builder Pattern Bradley.Schaefer@stitchfix.com @soulcutter
2. Experiments: Terminology Control Cell Experiment Cell
3. Experiments: Terminology A B
4. Experiments: Terminology loser WINNER
5. A/B Experiments The Way Things Were class BodyShape attr_reader :api, :client NAME = 'New Womens Body Shape Question' CONTROL_CELL = 'Control' TEST_CELL = 'New Question' def self.define! StitchFix::Experiments::API.define_experiment do name NAME treatment CONTROL_CELL, control: true treatment TEST_CELL end end def initialize(client) @api = StitchFix::Experiments::API.new(experiment_name: NAME, test_subject: client) @client = client end def show_new_body_shape_questions? api.allocating?(time: client.create_date) && api.in_cell?(cell_name: TEST_CELL) end end
6. A/B Experiments The Way Things Were class ItemTypeGroupPreferences attr_reader :api, :client NAME = 'New Womens Item Type Group Preferences' CONTROL_CELL = 'Control' TEST_CELL = 'New Question' def self.define! StitchFix::Experiments::API.define_experiment do name NAME treatment CONTROL_CELL, control: true treatment TEST_CELL end end def initialize(client) @api = StitchFix::Experiments::API.new(experiment_name: NAME, test_subject: client) @client = client end def show_new_womens_item_type_group_preferences_questions? api.allocating?(time: client.create_date) && api.in_cell?(cell_name: TEST_CELL) end end
7. A/B Experiments The Way Things Were class PrimaryObjectives attr_reader :api, :client NAME = 'New Womens Primary Reasons Question' CONTROL_CELL = 'Control' TEST_CELL = 'New Question' def self.define! StitchFix::Experiments::API.define_experiment do name NAME treatment CONTROL_CELL, control: true treatment TEST_CELL end end def initialize(client) @api = StitchFix::Experiments::API.new(experiment_name: NAME, test_subject: client) @client = client end def show_primary_objectives_question? api.allocating?(time: client.create_date) && api.in_cell?(cell_name: TEST_CELL) end end
8. A/B Experiments The Way Things Were class WomensBrands attr_reader :api, :client NAME = 'New Womens Brands Question' CONTROL_CELL = 'Control' TEST_CELL = 'New Question' def self.define! StitchFix::Experiments::API.define_experiment do name NAME treatment CONTROL_CELL, control: true treatment TEST_CELL end end def initialize(client) @api = StitchFix::Experiments::API.new(experiment_name: NAME, test_subject: client) @client = client end def show_womens_brands_question? api.allocating?(time: client.create_date) && api.in_cell?(cell_name: TEST_CELL) end end
9. A/B Experiments The Way Things Were class BottomsAttributePreferences attr_reader :api, :client NAME = 'New Womens Bottoms Attribute Preferences' CONTROL_CELL = 'Control' TEST_CELL = 'New Question' def self.define! StitchFix::Experiments::API.define_experiment do name NAME treatment CONTROL_CELL, control: true treatment TEST_CELL end end def initialize(client) @api = StitchFix::Experiments::API.new(experiment_name: NAME, test_subject: client) @client = client end def show_new_bottoms_attribute_preferences_question? api.allocating?(time: client.create_date) && api.in_cell?(cell_name: TEST_CELL) end end
10. What Stands Out?
11. What Stands Out? class BodyShape attr_reader :api, :client NAME = 'New Womens Body Shape Question' CONTROL_CELL = 'Control' TEST_CELL = 'New Question' def self.define! StitchFix::Experiments::API.define_experiment do name NAME treatment CONTROL_CELL, control: true treatment TEST_CELL end end def initialize(client) @api = StitchFix::Experiments::API.new( experiment_name: NAME, test_subject: client ) @client = client end def show_new_body_shape_questions? api.allocating?(time: client.create_date) && api.in_cell?(cell_name: TEST_CELL) end end class PrimaryObjectives attr_reader :api, :client NAME = 'New Womens Primary Reasons Question' CONTROL_CELL = 'Control' TEST_CELL = 'New Question' def self.define! StitchFix::Experiments::API.define_experiment do name NAME treatment CONTROL_CELL, control: true treatment TEST_CELL end end def initialize(client) @api = StitchFix::Experiments::API.new( experiment_name: NAME, test_subject: client ) @client = client end def show_primary_objectives_question? api.allocating?(time: client.create_date) && api.in_cell?(cell_name: TEST_CELL) end end
12. Duplication! class BodyShape attr_reader :api, :client NAME = 'New Womens Body Shape Question' CONTROL_CELL = 'Control' TEST_CELL = 'New Question' def self.define! StitchFix::Experiments::API.define_experiment do name NAME treatment CONTROL_CELL, control: true treatment TEST_CELL end end def initialize(client) @api = StitchFix::Experiments::API.new( experiment_name: NAME, test_subject: client ) @client = client end def show_new_body_shape_questions? api.allocating?(time: client.create_date) && api.in_cell?(cell_name: TEST_CELL) end end class PrimaryObjectives attr_reader :api, :client NAME = 'New Womens Primary Reasons Question' CONTROL_CELL = 'Control' TEST_CELL = 'New Question' def self.define! StitchFix::Experiments::API.define_experiment do name NAME treatment CONTROL_CELL, control: true treatment TEST_CELL end end def initialize(client) @api = StitchFix::Experiments::API.new( experiment_name: NAME, test_subject: client ) @client = client end def show_primary_objectives_question? api.allocating?(time: client.create_date) && api.in_cell?(cell_name: TEST_CELL) end end
13. Removing Duplication def initialize(client) @api = StitchFix::Experiments::API.new(experiment_name: NAME, test_subject: client) @client = client end
14. Removing Duplication module ABExperiment def initialize(client) @api = StitchFix::Experiments::API.new(experiment_name: NAME, test_subject: client) @client = client end end
15. Removing Duplication class BodyShape attr_reader :api, :client NAME = 'New Womens Body Shape Question' CONTROL_CELL = 'Control' TEST_CELL = 'New Question' def self.define! StitchFix::Experiments::API.define_experiment do name NAME treatment CONTROL_CELL, control: true treatment TEST_CELL end end def initialize(client) @api = StitchFix::Experiments::API.new(experiment_name: NAME, test_subject: client) @client = client end def show_new_body_shape_questions? api.allocating?(time: client.create_date) && api.in_cell?(cell_name: TEST_CELL) end end
16. Replace all initializers class BodyShape include ABExperiment attr_reader :api, :client NAME = 'New Womens Body Shape Question' CONTROL_CELL = 'Control' TEST_CELL = 'New Question' def self.define! StitchFix::Experiments::API.define_experiment do name NAME treatment CONTROL_CELL, control: true treatment TEST_CELL end end def initialize(client) @api = StitchFix::Experiments::API.new(experiment_name: NAME, test_subject: client) @client = client end def show_new_body_shape_questions? api.allocating?(time: client.create_date) && api.in_cell?(cell_name: TEST_CELL) end end
17. Looking better! class BodyShape include ABExperiment attr_reader :api, :client NAME = 'New Womens Body Shape Question' CONTROL_CELL = 'Control' TEST_CELL = 'New Question' def self.define! StitchFix::Experiments::API.define_experiment do name NAME treatment CONTROL_CELL, control: true treatment TEST_CELL allocation Time.now..6.months.from_now live true owner Client.first end end def show_new_body_shape_questions? api.allocating?(time: client.create_date) && api.in_cell?(cell_name: TEST_CELL) end end
18. But wait… there's a problem module ABExperiment def initialize(client) @api = StitchFix::Experiments::API.new(experiment_name: NAME, test_subject: client) @client = client end end
19. But wait… there's a problem module ABExperiment def initialize(client) @api = StitchFix::Experiments::API.new(experiment_name: NAME, test_subject: client) @client = client end end Let's run the tests…
20. But wait… there's a problem module ABExperiment def initialize(client) @api = StitchFix::Experiments::API.new(experiment_name: NAME, test_subject: client) @client = client end end Failure/Error: @api = StitchFix::Experiments::API.new(experiment_name: NAME, test_subject: client) NameError: uninitialized constant ABExperiment::NAME
21. But wait… there's a problem module ABExperiment def initialize(client) @api = StitchFix::Experiments::API.new(experiment_name: NAME, test_subject: client) @client = client end end Need a way to look up a constant in the correct scope
22. Scope? Credit: Craig McMillan 2008 https://mccraigmccraig.wordpress.com/2008/10/29/ruby-objects-classes-and-eigenclasses/
23. But wait… there's a problem module ABExperiment def initialize(client) @api = StitchFix::Experiments::API.new(experiment_name: NAME, test_subject: client) @client = client end end Failure/Error: @api = StitchFix::Experiments::API.new(experiment_name: NAME, test_subject: client) NameError: uninitialized constant ABExperiment::NAME
24. const_get does the trick module ABExperiment def initialize(client) @api = StitchFix::Experiments::API.new( experiment_name: self.class.const_get(:NAME), test_subject: client ) @client = client end end
25. What stands out now? class BodyShape include ABExperiment attr_reader :api, :client NAME = 'New Womens Body Shape Question' CONTROL_CELL = 'Control' TEST_CELL = 'New Question' def self.define! StitchFix::Experiments::API.define_experiment do name NAME treatment CONTROL_CELL, control: true treatment TEST_CELL end end def show_new_body_shape_questions? api.allocating?(time: client.create_date) && api.in_cell?(cell_name: TEST_CELL) end end
26. What stands out now? class BodyShape include ABExperiment attr_reader :api, :client NAME = 'New Womens Body Shape Question' CONTROL_CELL = 'Control' TEST_CELL = 'New Question' def self.define! StitchFix::Experiments::API.define_experiment do name NAME treatment CONTROL_CELL, control: true treatment TEST_CELL end end def show_new_body_shape_questions? api.allocating?(time: client.create_date) && api.in_cell?(cell_name: TEST_CELL) end end
27. Encapsulate api/client module ABExperiment attr_reader :api, :client def initialize(client) @api = StitchFix::Experiments::API.new( experiment_name: self.class.const_get(:NAME), test_subject: client ) @client = client end end
28. Encapsulate api/client class BodyShape include ABExperiment attr_reader :api, :client NAME = 'New Womens Body Shape Question' CONTROL_CELL = 'Control' TEST_CELL = 'New Question' def self.define! StitchFix::Experiments::API.define_experiment do name NAME treatment CONTROL_CELL, control: true treatment TEST_CELL end end def show_new_body_shape_questions? api.allocating?(time: client.create_date) && api.in_cell?(cell_name: TEST_CELL) end end
29. Looking even better! class BodyShape include ABExperiment NAME = 'New Womens Body Shape Question' CONTROL_CELL = 'Control' TEST_CELL = 'New Question' def self.define! StitchFix::Experiments::API.define_experiment do name NAME treatment CONTROL_CELL, control: true treatment TEST_CELL end end def show_new_body_shape_questions? api.allocating?(time: client.create_date) && api.in_cell?(cell_name: TEST_CELL) end end
30. What stands out now? class BodyShape include ABExperiment NAME = 'New Womens Body Shape Question' CONTROL_CELL = 'Control' TEST_CELL = 'New Question' def self.define! StitchFix::Experiments::API.define_experiment do name NAME treatment CONTROL_CELL, control: true treatment TEST_CELL end end def show_new_body_shape_questions? api.allocating?(time: client.create_date) && api.in_cell?(cell_name: TEST_CELL) end end
31. What stands out now? class BodyShape include ABExperiment NAME = 'New Womens Body Shape Question' CONTROL_CELL = 'Control' TEST_CELL = 'New Question' def self.define! StitchFix::Experiments::API.define_experiment do name NAME treatment CONTROL_CELL, control: true treatment TEST_CELL end end def show_new_body_shape_questions? api.allocating?(time: client.create_date) && api.in_cell?(cell_name: TEST_CELL) end end
32. We can extract that too! module ABExperiment extend ActiveSupport::Concern # ... module ClassMethods def define! StitchFix::Experiments::API.define_experiment do name NAME treatment CONTROL_CELL, control: true treatment TEST_CELL end end end end
33. Oh yeah, I've seen this before module ABExperiment extend ActiveSupport::Concern # ... module ClassMethods def define! StitchFix::Experiments::API.define_experiment do name NAME treatment CONTROL_CELL, control: true treatment TEST_CELL end end end end
34. Oh yeah, I've seen this before module ABExperiment extend ActiveSupport::Concern # ... module ClassMethods def define! StitchFix::Experiments::API.define_experiment do name const_get(:NAME) treatment const_get(:CONTROL_CELL), control: true treatment const_get(:TEST_CELL) end end end end
35. Oh yeah, I've seen this before module ABExperiment extend ActiveSupport::Concern # ... module ClassMethods def define! StitchFix::Experiments::API.define_experiment do name const_get(:NAME) treatment const_get(:CONTROL_CELL), control: true treatment const_get(:TEST_CELL) end end end end Let's run the tests…
36. This is new… Failure/Error: name const_get(:NAME) NoMethodError: undefined method `const_get' for #<StitchFix::Experiments::DSL: 0x007fc103dc8e28>
37. Not the expected scope Failure/Error: name const_get(:NAME) NoMethodError: undefined method `const_get' for #<StitchFix::Experiments::DSL: 0x007fc103dc8e28> def define! StitchFix::Experiments::API.define_experiment do name const_get(:NAME) treatment const_get(:CONTROL_CELL), control: true treatment const_get(:TEST_CELL) end end
38. Let's fix that Failure/Error: name const_get(:NAME) NoMethodError: undefined method `const_get' for #<StitchFix::Experiments::DSL: 0x007fc103dc8e28> def define! klass = self StitchFix::Experiments::API.define_experiment do name klass.const_get(:NAME) treatment klass.const_get(:CONTROL_CELL), control: true treatment klass.const_get(:TEST_CELL) end end
39. module ABExperiment extend ActiveSupport::Concern attr_reader :client, :api def initialize(client) @client = client @api = StitchFix::Experiments::API.new( experiment_name: self.class.const_get(:NAME), test_subject: client ) end module ClassMethods def define! klass = self StitchFix::Experiments::API.define_experiment do name klass.const_get(:NAME) treatment klass.const_get(:CONTROL_CELL), control: true treatment klass.const_get(:TEST_CELL) end end end end
40. Looking really good! class BodyShape include ABExperiment NAME = 'New Womens Body Shape Question' CONTROL_CELL = 'Control' TEST_CELL = 'New Question' def show_new_body_shape_questions? api.allocating?(time: client.create_date) && api.in_cell?(cell_name: TEST_CELL) end end
41. But Wait, There's MORE!
42. There's something still bothering me class BodyShape include ABExperiment NAME = 'New Womens Body Shape Question' CONTROL_CELL = 'Control' TEST_CELL = 'New Question' def show_new_body_shape_questions? api.allocating?(time: client.create_date) && api.in_cell?(cell_name: TEST_CELL) end end
43. An Encapsulation Problem class BodyShape include ABExperiment NAME = 'New Womens Body Shape Question' CONTROL_CELL = 'Control' TEST_CELL = 'New Question' def show_new_body_shape_questions? api.allocating?(time: client.create_date) && api.in_cell?(cell_name: TEST_CELL) end end
44. The Module Builder Pattern! class BodyShape include ABExperimentBuilder.new( name: 'New Womens Body Shape Question', control_cell: 'Control', test_cell: 'New Question' ) def show_new_body_shape_questions? api.allocating?(time: client.create_date) && api.in_cell?(cell_name: TEST_CELL) end end
45. class ABExperimentBuilder < Module def initialize(name:, test_cell:, control_cell: 'Control') const_set(:NAME, name) const_set(:CONTROL_CELL, control_cell) const_set(:TEST_CELL, test_cell) attr_reader :api, :client define_method(:initialize) do |client| @client = client @api = StitchFix::Experiments::API.new( experiment_name: self.class.const_get(:NAME), test_subject: client ) end end module ClassMethods def define! klass = self StitchFix::Experiments::API.define_experiment do name klass.const_get(:NAME) treatment klass.const_get(:CONTROL_CELL), control: true treatment klass.const_get(:TEST_CELL) end end end def included(base) base.extend ClassMethods end end
46. We did it!
47. class ABExperimentBuilder < Module def initialize(name:, test_cell:, control_cell: 'Control') const_set(:NAME, name) const_set(:CONTROL_CELL, control_cell) const_set(:TEST_CELL, test_cell) attr_reader :api, :client define_method(:initialize) do |client| @client = client @api = StitchFix::Experiments::API.new( experiment_name: self.class.const_get(:NAME), test_subject: client ) end end module ClassMethods def define! klass = self StitchFix::Experiments::API.define_experiment do name klass.const_get(:NAME) treatment klass.const_get(:CONTROL_CELL), control: true treatment klass.const_get(:TEST_CELL) end end end def included(base) base.extend ClassMethods end end
48. Extending Module? class ABExperimentBuilder < Module
49. Module is a Class module ABExperiment # … end ABExperiment = Module.new do # … end
50. Why extend Module? class ABExperimentBuilder < Module Instances of ABExperimentBuilder can be treated like a Module
51. class ABExperimentBuilder < Module def initialize(name:, test_cell:, control_cell: 'Control') const_set(:NAME, name) const_set(:CONTROL_CELL, control_cell) const_set(:TEST_CELL, test_cell) attr_reader :api, :client define_method(:initialize) do |client| @client = client @api = StitchFix::Experiments::API.new( experiment_name: self.class.const_get(:NAME), test_subject: client ) end end module ClassMethods def define! klass = self StitchFix::Experiments::API.define_experiment do name klass.const_get(:NAME) treatment klass.const_get(:CONTROL_CELL), control: true treatment klass.const_get(:TEST_CELL) allocation Time.now..6.months.from_now live true owner Client.first end end end def included(base) base.extend ClassMethods end end
52. Configuring a Module def initialize(name:, test_cell:, control_cell: 'Control') const_set(:NAME, name) const_set(:CONTROL_CELL, control_cell) const_set(:TEST_CELL, test_cell) attr_reader :api, :client define_method(:initialize) do |client| @client = client @api = StitchFix::Experiments::API.new( experiment_name: self.class.const_get(:NAME), test_subject: client ) end end
53. Configuring a Module def initialize(name:, test_cell:, control_cell: 'Control') const_set(:NAME, name) const_set(:CONTROL_CELL, control_cell) const_set(:TEST_CELL, test_cell) attr_reader :api, :client define_method(:initialize) do |client| @client = client @api = StitchFix::Experiments::API.new( experiment_name: self.class.const_get(:NAME), test_subject: client ) end end
54. Configuring a Module def initialize(name:, test_cell:, control_cell: 'Control') const_set(:NAME, name) const_set(:CONTROL_CELL, control_cell) const_set(:TEST_CELL, test_cell) attr_reader :api, :client define_method(:initialize) do |client| @client = client @api = StitchFix::Experiments::API.new( experiment_name: self.class.const_get(:NAME), test_subject: client ) end end
55. Configuring a Module def initialize(name:, test_cell:, control_cell: 'Control') const_set(:NAME, name) const_set(:CONTROL_CELL, control_cell) const_set(:TEST_CELL, test_cell) attr_reader :api, :client define_method(:initialize) do |client| @client = client @api = StitchFix::Experiments::API.new( experiment_name: self.class.const_get(:NAME), test_subject: client ) end end
56. Configuring a Module def initialize(name:, test_cell:, control_cell: 'Control') const_set(:NAME, name) const_set(:CONTROL_CELL, control_cell) const_set(:TEST_CELL, test_cell) attr_reader :api, :client define_method(:initialize) do |client| @client = client @api = StitchFix::Experiments::API.new( experiment_name: self.class.const_get(:NAME), test_subject: client ) end end ABExperimentBuilder.new( name: 'New Womens Body Shape Question', test_cell: 'New Question' )
57. Template for Building Modules module ABExperimentTemplate NAME = 'Foo' CONTROL_CELL = 'Control' TEST_CELL = 'Test' attr_reader :api, :client def initialize(client) @client = client @api = StitchFix::Experiments::API.new( experiment_name: NAME, test_subject: client ) end end ABExperimentBuilder.new( name: 'Foo', test_cell: 'Test', control_cell: 'Control' ) {
58. Template for Building Modules module ABExperimentTemplate NAME = 'Foo' CONTROL_CELL = 'Control' TEST_CELL = 'Test' attr_reader :api, :client def initialize(client) @client = client @api = StitchFix::Experiments::API.new( experiment_name: NAME, test_subject: client ) end end ABExperimentBuilder.new( name: 'Foo', test_cell: 'Test', control_cell: 'Control' ) {
59. Template for Building Modules module ABExperimentTemplate NAME = 'Foo' CONTROL_CELL = 'Control' TEST_CELL = 'Test' attr_reader :api, :client def initialize(client) @client = client @api = StitchFix::Experiments::API.new( experiment_name: NAME, test_subject: client ) end end ABExperimentBuilder.new( name: 'Foo', test_cell: 'Test', control_cell: 'Control' ) {
60. What about the class methods?
61. class ABExperimentBuilder < Module def initialize(name:, test_cell:, control_cell: 'Control') const_set(:NAME, name) const_set(:CONTROL_CELL, control_cell) const_set(:TEST_CELL, test_cell) attr_reader :api, :client define_method(:initialize) do |client| @client = client @api = StitchFix::Experiments::API.new( experiment_name: self.class.const_get(:NAME), test_subject: client ) end end module ClassMethods def define! klass = self StitchFix::Experiments::API.define_experiment do name klass.const_get(:NAME) treatment klass.const_get(:CONTROL_CELL), control: true treatment klass.const_get(:TEST_CELL) allocation Time.now..6.months.from_now live true owner Client.first end end end def included(base) base.extend ClassMethods end end
62. You don't need a Concern module ClassMethods # … end def included(base) base.extend ClassMethods end
63. The Final Result class BodyShape include ABExperimentBuilder.new( name: 'New Womens Body Shape Question', control_cell: 'Control', test_cell: 'New Question' ) def show_new_body_shape_questions? api.allocating?(time: client.create_date) && api.in_cell?(cell_name: TEST_CELL) end end
64. The Interesting Bits, Front and Center class BodyShape include ABExperimentBuilder.new( name: 'New Womens Body Shape Question', control_cell: 'Control', test_cell: 'New Question' ) def show_new_body_shape_questions? api.allocating?(time: client.create_date) && api.in_cell?(cell_name: TEST_CELL) end end
65. Module Builder Tradeoffs Good Bad Experiment Class Readability I wrote a talk to explain the code in ABExperimentBuilder Can test module builder code and be confident it works across all experiments Too much magic? It's a neat Ruby technique metaprogramming: bad Didn't change tests/interface Changing interface potentially valuable
66. Alternatives
67. Configuring via a method class BodyShape include ABExperiment ab_experiment( name: 'New Womens Body Shape Question', control_cell: 'Control', test_cell: 'New Question' ) def show_new_body_shape_questions? api.allocating?(time: client.create_date) && api.in_cell?(cell_name: TEST_CELL) end end
68. Config Method Tradeoffs Good Bad A more-familiar-looking pattern? Just as much if not more metaprogramming Have to jump through hoops to NOT define methods directly on the class If you define methods on the class, no ability to override behavior via super I didn't write a talk about that
69. Credits Chris Salzberg http://dejimata.com/2017/5/20/the-ruby-module-builder-pattern Gal Steinitz
70. Questions?
71. Applying the Module Builder Pattern Bradley.Schaefer@stitchfix.com @soulcutter