Immortal Ruby

Talk about Immutability and Ruby presented on RubyNation 2014

Transcript

1. Immortal Ruby
2. Marcos Matos
3. marcosccm
4. ThoughtWorks
5. Immutability
6. Have you tried rebooting the server? ! the complete guide to fixing software
7. “Cool! The problem magically fixed itself” ! Do you really believe in that?
8. It’s a BUG!
9. I would have written simpler code, but I did not have the time. ! Blaise Pascal (or maybe Mark Twain, or Newton) on writing code
10. The path of the bug is full of complexity and misunderstanding ! or anger and small paychecks
11. Many smart folks believe that our dependency on mutable state is a huge cause of complexity ! See all of Rich Hickey’s presentations…
12. mutable state led us to the TAR PIT
13. state makes ! Reasoning hard Testing hard Concurrency hard Life hard
14. I must not mutate state. State is the code-killer. State is the little-death that brings total complication. ! The Litany against State
15. but that’s how I learned how to program!
16. atual <- 1! ant <- 0! repita! num <- atual + ant! escreva ("num")! ant <- atual! atual <- num! cont <- cont + 1! ate (cont = n-2) The (not really) amazing Portugol
17. small caveat
18. we need some state!
19. we call it user input ! users are sadly not referentially transparent
20. Data vs State
21. Data ! Things your application needs in order to work
22. State ! all the mutations we impose on our data without necessity
23. so how do one atone for his sinful stateful ways?
24. Solution #1 ! write everything in Haskell
25. no, I want to keep using Ruby
26. Solution #2 ! just mutate less stuff
27. nothing in Ruby prevents you from writing immutable code
28. nothing helps either…
29. Why is so hard to write immutable OO code?
30. Values vs Identity
31. Values ! Atomic concepts that cannot change
32. Values ! 42, phone numbers, dates
33. Identity ! A logical entity composed by values that change over time
34. Identity ! you, me, your bank account
35. How Ruby handles this?
36. > 42 => 42 ! => 42.next > 43 ! > n = 42 > n = n + 1 => 43 ! > 42 = 42 + 1 => WhatTheHellAreYouDoingError You can’t change natural numbers
37. > dish1 = “potato” > dish2 = dish1 > dish1[0] = “d” ! > puts dish1 => “dotato” ! > puts dish2 => “dotato” You can, however, redefine the Scottish cuisine
38. > col1 = [1,2,3] > col2 = col1 > col1 << 4 ! > puts col1 => [1,2,3,4] ! > puts col2 => [1,2,3,4] Arrays suffer the same fate
39. how we avoid mutating our values?
40. > dish1 = “potato” > dish2 = dish1 ! > dish1 = dish1.sub(’b’,’d’) ! > puts dish1 => “dotato” ! > puts dish2 => “potato” avoid the !
41. > col1 = [1,2,3] > col2 = col1.dup > col1 << 4 ! > puts col1 => [1,2,3,4] ! > puts col2 => [1,2,3] the attack of the clones
42. > glasgow = “rainy” > glasgow.freeze ! > glasgow.sub!(“rainy”, “sunny”) => Can’t modify frozen String (RunTimeError) What killed the dinosaurs? The Ice Age! Mr Freeze
43. > iceberg = [”big”,”chunk”,”ice”] > iceberg.freeze ! > iceberg.shift(“very”) => RuntimeError: can't modify frozen Array ! > iceberg[0].sub!(“big”, “small”) => [”small”,”chunk”,”ice”] more like Array#chill_out
44. > require ‘ice_nine' ! > iceberg = [”big”,”chunk”,”ice”] > IceNine.deep_freeze(iceberg) ! > iceberg.shift(“very”) => RuntimeError: can't modify frozen Array ! > iceberg[0].sub!(“big”, “small”) => RuntimeError: can't modify frozen String github.com/dkubb/ice_nine
45. > require ‘hamster' ! > addr = Hamster.hash(street: ‘Queen St’, number: ‘152’) => { :street => ‘Queen St’, :number => ‘152’ } ! > with_city = addr.put(:city, ‘Glasgow’) => { :street => ‘..’, :number => ‘..’, city => ‘Glasgow’ } ! > addr => { :street => ‘Queen St’, :number => ‘152’ } https://github.com/hamstergem/hamster
46. > require ‘hamster' ! > without_city = addr.delete(:city) => { :street => ‘Queen St’, :number => ‘152’ } ! > with_city => { :street => ‘..’, :number => ‘..’, city => ‘Glasgow’ } https://github.com/hamstergem/hamster
47. what about more complex objects?
48. Value Objects ! Objects that are defined by the total of their values
49. Don’t give a value object any identity and avoid the design complexities necessary to maintain entities. Eric Evans on value objects
50. class Address attr_reader :street, :complement, :city ! def initialize(street, complement, city) @street = street @complement = complement @city = city end ! def to_s "#{street}, #{complement}, #{city}" end end A boring Address
51. > address = Address.new(“Queen st”, “a secret”, “Glasgow”) > puts address => “Queen St, a secret, Glasgow” ! > addess.street = “Argyle St” => bla undefined method street=bla bla ! > address.street.gsub!(/Queen/,”Lolz”) > puts address => “Lolz St, a secret, Glasgow” Lolz Encapsulation
52. require 'ice_nine' ! class Address attr_reader :street, :complement, :city ! def initialize(street, complement, city) @street = street @complement = complement @city = city IceNine.deep_freeze!(self) end ! def to_s "#{street}, #{complement}, #{city}" end end Immutability at last!
53. require 'virtus' ! class Address include Virtus.value_object ! values do attribute :street, String attribute :complement, String attribute :city, String end end github.com/solnic/virtus
54. Hurray! ! We have Immutable Addresses!
55. what about our core domain objects?
56. Objects a collection of state and methods that operate on top of that state
57. class BankAccount attr_reader :current ! def initialize @current = 0 end ! def deposit(amount) @current = current + amount end ! def withdrawal(amount) @current = current - amount end end a robust banking system
58. Objects a snapshot of state and methods that exposes possibilities on top of that state
59. class BankAccount attr_reader :current ! def initialize(current) @current = current end ! def deposit(amount) BankAccount.new(current + amount) end ! def withdrawal(amount) BankAccount.new(current - amount) end end no mutations
60. we can reduce state mutation where it really matters!
61. what about Active Record?
62. class Address < ActiveRecord::Base attr_readonly :street attr_readonly :complement attr_readonly :city end good guy active record
63. > address = Address.create(street: “Queen st”) > Address.first.street => “Queen St” ! > addess.update_attributes(street: “Argyle St”) > address.street => “Argyle St” ! > Address.find(1).street => “Queen St” bug or feature?
64. what about performance?
65. Immutability everywhere
66. Immutable Databases Datomic ! Immutable Frontend ClojureScript
67. Recap
68. Mutable state brings complexity
69. We can have Immutability in Ruby
70. go beyond Value Objects
71. Wanna learn more? ! Amazing blog post from the author of the Hamster lib http://www.harukizaemon.com/blog/2010/03/01/functional-programming-in-object-oriented- languages/ ! Anything Rich Hickey http://thechangelog.com/rich-hickeys-greatest-hits/ ! The Tar Pit paper http://shaffner.us/cs/papers/tarpit.pdf ! Clojure’s take on State http://clojure.org/state
72. Obrigado!
73. Discussion Time!