From OO to FP

A journey from messy strategy pattern to functional concepts in Ruby.

Transcript

1. From OO to FP without killing yourself @rusilko Tomek Rusiłko
2. about me 3 facts
3. Krakow, Poland #1
4. Krakow, Poland #1 Krakow Ruby User Group
5. #2
6. #3 I am an object-oriented Ruby programmer. surprise?
7. I am an object-oriented programmer thanks to Ruby.
8. Dense Low ceremony Fully object oriented
10. Ruby is an enabler.
11. functional = Black.new
13. … concurrency, monad, functor, monad, applicative, comonad, concurrency, contravariant monad …
15. business context
16. mortgage broker app
20. credit score
21. Credit Score
22. def score a = @property.input_1 + @property.input_2 b = (@borrower.input_1 * @bank.param_1) / 4 c = (a / b) * @mortgage.input_1 d = if c > @bank.min_value (@bank.param_2 * @mortgage.input_3) else 0 end # . . . y = . . . z = . . . score = [ y/z, u ] score end
23. def score a = @property.input_1 + @property.input_2 b = (@borrower.input_1 * @bank.param_1) / 4 c = (a / b) * @mortgage.input_1 d = if c > @bank.min_value (@bank.param_2 * @mortgage.input_3) else 0 end # . . . y = . . . z = . . . score = [ y/z, u ] score end
24. def score a = @property.input_1 + @property.input_2 b = (@borrower.input_1 * @bank.param_1) / 4 c = (a / b) * @mortgage.input_1 d = if c > @bank.min_value (@bank.param_2 * @mortgage.input_3) else 0 end # . . . y = . . . z = . . . score = [ y/z, u ] score end
25. def score a = @property.input_1 + @property.input_2 b = (@borrower.input_1 * @bank.param_1) / 4 c = (a / b) * @mortgage.input_1 d = if c > @bank.min_value (@bank.param_2 * @mortgage.input_3) else 0 end # . . . y = . . . z = . . . score = [ y/z, u ] score end
26. def score a = @property.input_1 + @property.input_2 b = (@borrower.input_1 * @bank.param_1) / 4 c = (a / b) * @mortgage.input_1 d = if c > @bank.min_value (@bank.param_2 * @mortgage.input_3) else 0 end # . . . y = . . . z = . . . score = [ y/z, u ] score end
27. def score a = @property.input_1 + @property.input_2 b = (@borrower.input_1 * @bank.param_1) / 4 c = (a / b) * @mortgage.input_1 d = if c > @bank.min_value (@bank.param_2 * @mortgage.input_3) else 0 end # . . . y = . . . z = . . . score = [ y/z, w ] score end
28. def score a = @property.input_1 + @property.input_2 b = (@borrower.input_1 * @bank.param_1) / 4 c = (a / b) * @mortgage.input_1 d = if c > @bank.min_value (@bank.param_2 * @mortgage.input_3) else 0 end # . . . y = . . . z = . . . score = [ y/z, w ] score end
29. def score a = @property.input_1 + @property.input_2 b = (@borrower.input_1 * @bank.param_1) / 4 c = (a / b) * @mortgage.input_1 d = if c > @bank.min_value (@bank.param_2 * @mortgage.input_3) else 0 end # . . . y = . . . z = . . . score = [ y/z, w ] score end
30. SCORE
31. class ScoreCalculator def initialize(property, mortgage, borrower, settings, bank) @property = property @mortgage = mortgage @bank = bank # . . . end def score a = @property.input_1 + @property.input_2 # . . . [y/z, w] end end
32. class ScoreCalculator def initialize(property, mortgage, borrower, settings, bank) @property = property @mortgage = mortgage @bank = bank # . . . end def score a = @property.input_1 + @property.input_2 # . . . [y/z, w] end end
33. class ScoreCalculator def initialize(property, mortgage, borrower, settings, bank) @property = property @mortgage = mortgage @bank = bank # . . . end def score a = @property.input_1 + @property.input_2 # . . . [y/z, w] end end
34. class ScoreCalculator def initialize(property, mortgage, borrower, settings, bank) @property = property @mortgage = mortgage @bank = bank # . . . end def score a = @property.input_1 + @property.input_2 # . . . [y/z, w] end end
35. class ScoreCalculator def initialize(property, mortgage, borrower, settings, bank) def score [y/z, w] end private def y def z # . . . def b def a end
36. class ScoreCalculator def initialize(property, mortgage, borrower, settings, bank) def score [y/z, w] end private def borrower_total_income @borrower.basic_income + 
 @borrower.additional_income + @borrower.bonus_income end end
37. class Borrower < ActiveRecord::Base def initialize(property, mortgage, borrower, settings, bank) def score [y/z, w] end private def borrower_total_income @borrower.basic_income + 
 @borrower.additional_income + @borrower.bonus_income end end
38. class Borrower < ActiveRecord::Base def initialize(property, mortgage, borrower, settings, bank) def score [y/z, w] end private def total_income basic_income + 
 additional_income + bonus_income end end
39. class ScoreCalculator def initialize(property, mortgage, borrower, settings, bank) def score [y/z, w] end private def borrower_income @borrower.income + 
 @borrower.additional_income + @borrower.bonus_income end end
40. SCORE ScoreCalculator
41. class InvestitureCalculator def initialize(property, mortgage, bank) @property = property @mortgage = mortgage @bank = bank end def investiture (d / e) ^ @bank.investiture_factor end private def d; end def e; end end
42. SCORE ScoreCalculator Investiture B G P W
43. new features
44. bank report
45. SCORE ScoreCalculator A F K P W
46. new banks
47. id name param_1 param_2 param_3 … 1 bankA 0.6 55 0.75 … 2 bankB 0.66 60 0.75 … 3 bankC 0.65 60 0.65 … … … … … … …
48. class Borrower < ActiveRecord::Base def initialize(property, mortgage, borrower, settings, bank) def total_income basic_income + 
 additional_income + bonus_income end end
49. class Borrower < ActiveRecord::Base def initialize(property, mortgage, borrower, settings, bank) def total_income basic_income + 
 additional_income + bonus_income * 0.5 end end
50. class ScoreCalculator def borrower_total_income @borrower.basic_income + 
 @borrower.additional_income + @borrower.bonus_income * @bank.bonus_factor end end
51. id name param_1 param_2 param_3 bonus_factor 1 bankA 0.6 55 0.75 1 2 bankB 0.66 60 0.75 1 3 bankC 0.65 60 0.65 0.5 … … … … … …
52. strategy pattern
53. SCORE ScoreCalculator A F K P W
54. SCORE ScoreCalculator A P F K P W
55. class NewBank::AmortizationStrategy def amortization # new_formula end end class Default:AmortizationStrategy def amortization # old_formula end end
56. class NewBank::AmortizationStrategy def amortization # new_formula end end class Default:AmortizationStrategy def amortization # old_formula end end
57. class NewBank::AmortizationStrategy def initialize(different collaborators) # end end class Default:AmortizationStrategy def initialize(collaborators) # end end
58. SCORE ScoreCalculator A F K W P
59. SCORE ScoreCalculator A F K W P P
60. P SCORE ScoreCalculator A F K W P
61. P SCORE ScoreCalculator A F K W P K
62. P SCORE ScoreCalculator A F K W P K
63. Can you feel the pain?
65. • coding is not fun • slow velocity • demotivated team • long new developer ramp-up • bus factor
67. Symptoms • coding is not fun • slow velocity • demotivated team • long new developer ramp-up • low bus factor
71. input_data = { property_input_1: 10, property_input_2: 20, borrower_input_1: 30, mortgage_input_1: true . . . }
72. property_input_1 property.input_1
74. class BankA def parameters { bank_param_1: 0.6, bank_param_2: 60, } end end class BankB def parameters { bank_param_1: 0.5, bank_param_2: 65 } end end
75. P SCORE ScoreCalculator A F K W P K
78. First class citizens
79. b = lambda { |data| data[:borrower_input_1] * data[:mortgage_input_2] } # Call it b.call(data) b.(data)
80. module B def self.call(data) data[:borrower_input_1] * data[:mortgage_input_2] end end B.call(data) B.(data)
81. module B def self.call(borrower_input_1:, mortgage_input_2:) borrower_input_1 * mortgage_input_2 end end B.call(data) B.(data)
82. module B def self.call(borrower_input_1:, mortgage_input_2:, **kwargs) borrower_input_1 * mortgage_input_2 end end B.call(data) B.(data)
83. module B def self.call(borrower_input_1:, mortgage_input_2:, **_) borrower_input_1 * mortgage_input_2 end end B.call(data) B.(data)
85. def evaluation_pipeline { a: A, b: B, . . . score: Score, } end
87. class BankA def parameters; end; def evaluation_pipeline { a: A, b: B,
 . . . score: Score, } end end
88. class BankB def parameters; end; def evaluation_pipeline { a: A, b: BankB::B,
 .
 .
 . score: BankB::Score, } end end
93. class ScoreCalculator def self.call(input_data, bank) data = input_data.merge(bank.parameters) pipe = bank.evaluation_pipeline pipe.each do |name, calculate| result = calculate.(data) new_pair = { name => result } data = data.merge(new_pair) end data end end Evaluate.(input_data, bank)
94. module Evaluate def self.call(input_data, bank) data = input_data.merge(bank.parameters) pipe = bank.evaluation_pipeline pipe.each do |name, calculate| result = calculate.(data) new_pair = { name => result } data = data.merge(new_pair) end data end end Evaluate.(input_data, bank)
95. module Evaluate def self.call(input_data, bank) data = input_data.merge(bank.parameters) pipe = bank.evaluation_pipeline pipe.each do |name, calculate| result = calculate.(data) new_pair = { name => result } data = data.merge(new_pair) end data end end Evaluate.(input_data, bank)
96. module Evaluate def self.call(input_data, bank) data = input_data.merge(bank.parameters) pipe = bank.evaluation_pipeline pipe.each do |name, calculate| result = calculate.(data) new_pair = { name => result } data = data.merge(new_pair) end data end end Evaluate.(input_data, bank)
97. module Evaluate def self.call(input_data, bank) data = input_data.merge(bank.parameters) pipe = bank.evaluation_pipeline pipe.each do |name, calculate| result = calculate.(data) new_pair = { name => result } data = data.merge(new_pair) end data end end Evaluate.(input_data, bank)
98. module Evaluate def self.call(input_data, bank) data = input_data.merge(bank.parameters) pipe = bank.evaluation_pipeline pipe.each do |name, calculate| result = calculate.(data) new_pair = { name => result } data = data.merge(new_pair) end data end end Evaluate.(input_data, bank)
99. module Evaluate def self.call(input_data, bank) data = input_data.merge(bank.parameters) pipe = bank.evaluation_pipeline pipe.each do |name, calculate| result = calculate.(data) new_pair = { name => result } data = data.merge(new_pair) end data end end Evaluate.(input_data, bank)
100. module Evaluate def self.call(input_data, bank) data = input_data.merge(bank.parameters) pipe = bank.evaluation_pipeline pipe.each do |name, calculate| result = calculate.(data) new_pair = { name => result } data = data.merge(new_pair) end data end end Evaluate.(input_data, bank)
101. module Evaluate def self.call(input_data, bank) data = input_data.merge(bank.parameters) pipe = bank.evaluation_pipeline pipe.reduce(data) do |data, (name, calculate)| data.merge(name => calculate.(data)) end end end Evaluate.(input_data, bank)
102. output_data = { property_input_1: 10, property_input_2: 20, borrower_input_1: 30, mortgage_input_1: true, bank_param_1: 0.6, bank_param_2: 60, a: 60, b: 18.2, x: . . ., y: . . ., score: “A” }
103. simple & extensible composable, with clear boundaries intent revealing
105. lessons learned
106. • FP is about stateless, composable functions working on immutable data structures. And it can be a powerful concept to have in your toolbox. • While every problem can be solved with OO, it’s not the only and best solution out there. • Some OO design patterns are workarounds of missing language features like first class functions.
107. Some references • https://www.sitepoint.com/functional-programming- techniques-with-ruby-part-i/ • https://leanpub.com/fp-oo • http://blog.cleancoder.com/uncle-bob/2014/11/24/ FPvsOO.html • http://loup-vaillant.fr/tutorials/from-imperative-to- functional • Programming Elixir by Dave Thomas
108. Ruby is an enabler.
109. Thank you @rusilko Tomek Rusiłko functional cats by Gosia Nowak, @designaur