Applying the Module Builder Pattern Bradley.Schaefer@stitchfix.com @soulcutter 

Experiments: Terminology Control Cell Experiment Cell 

Experiments: Terminology A B 

Experiments: Terminology loser WINNER 

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 

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 

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 

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 

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 

What Stands Out? 

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 

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 

Removing Duplication def initialize(client) @api = StitchFix::Experiments::API.new(experiment_name: NAME, test_subject: client) @client = client end 

Removing Duplication module ABExperiment def initialize(client) @api = StitchFix::Experiments::API.new(experiment_name: NAME, test_subject: client) @client = client end end 

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 

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 

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 

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 

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… 

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 

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 

Scope? Credit: Craig McMillan 2008 https://mccraigmccraig.wordpress.com/2008/10/29/ruby-objects-classes-and-eigenclasses/ 

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 

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 

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 

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 

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 

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 

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 

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 

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 

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 

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 

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 

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… 

This is new… Failure/Error: name const_get(:NAME) NoMethodError: undefined method `const_get' for # 

Not the expected scope Failure/Error: name const_get(:NAME) NoMethodError: undefined method `const_get' for # 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 

Let's fix that Failure/Error: name const_get(:NAME) NoMethodError: undefined method `const_get' for # 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 

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 

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 

But Wait, There's MORE! 

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 

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 

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 

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 

We did it! 

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 

Extending Module? class ABExperimentBuilder < Module 

Module is a Class module ABExperiment # … end ABExperiment = Module.new do # … end 

Why extend Module? class ABExperimentBuilder < Module Instances of ABExperimentBuilder can be treated like a Module 

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 

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 

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 

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 

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 

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' ) 

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' ) { 

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' ) { 

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' ) { 

What about the class methods? 

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 

You don't need a Concern module ClassMethods # … end def included(base) base.extend ClassMethods end 

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 

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 

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 

Alternatives 

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 

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 

Credits Chris Salzberg http://dejimata.com/2017/5/20/the-ruby-module-builder-pattern Gal Steinitz 

Questions? 

Applying the Module Builder Pattern Bradley.Schaefer@stitchfix.com @soulcutter