Why doesn't Ruby have Boolean class - final version

https://friendlyrb.com
This is a talk given at Friendly.rb 2025

1. Why doesn't Ruby have Boolean class? Friendly.rb 2025 OKURA Masafumi, 2025-09-10
2. Disclaimer: NO AI!!!!!!!!!!
3. Bună ziua!
4. ͳͥRubyʹ͸BooleanΫϥε ͕ͳ͍ͷ͔ BuriKaigi 2024 OKURA Masafumi, 2024-01-20
5. ͳͥRubyʹ͸BooleanΫϥε ͕ͳ͍ͷ͔ BuriKaigi 2024 OKURA Masafumi, 2024-01-20
6. BuriKaigi
7. BooleanKaigi?
9. introduce(self) • Name: OKURA Masafumi • From: Tokyo, Japan • Work: Freelancer • Activity: Kaigi on Rails (Founder, chief organizer), speaker (RubyConf Tw 2023/2025, EuRuKo 2023, Red Dot Ruby Conference 2024, Rails World 2025, Friendly.rb 2025), OSS (Alba and a few others) • Favorite method: `BasicObject#instance_eval`
14. Why Doesn’t Ruby have Boolean class?
15. I’m going to talk about… 1. Fact: How Ruby implements Boolean-related classes and methods 2. Opinion: Why don’t we need Boolean class with Ruby
16. Takeaways:
17. The takeaways of this talk are… • The “Ruby Way” about Boolean • Know more about language • The design principle of programming languages • Decision of NOT adding Boolean class • (And How Matz thinks about this???) • (In the original talk, Matz wasn’t there)
18. 1. Fact
19. Demo!
20. Boolean-related facts in Ruby • TrueClass and FalseClass are the class for true and false object, respectively • These classes are “singleton” classes that have only one instance, not having `new` method • TrueClass and FalseClass don’t have a common parent class • There is no method such as `to_bool`, but we can use `!!expr` idiom • Any object, not only true and false, can be used with `if` expression (false and `nil` are falsy, every other object including empty string and 0 are truthy)
21. Other languages • There are “immediate values” (Java) • true and false are immediate values (not objects, no classes) in Java • In some languages, only `true` and `false` can be used for `if` statement (Java, Haskell, etc.) • In some languages, there are methods to convert objects into boolean values (Python, JavaScript, etc.)
22. In Ruby, everything is object
23. In Ruby, every object has its Class
24. Singleton classes: TrueClass FalseClass NilClass
25. They exist, but not for practical reasons
26. v.is_a? (TrueClass) v == true
27. 2. Opinion
28. We don’t need Boolean class!
29. https://bugs.ruby- lang.org/issues/ 12515
30. > Create "Boolean" superclass of TrueClass / FalseClass
31. Status: Rejected
32. Rejected for several reasons: many gems and libraries had already introduced Boolean class. I don't want to break them. true and false are the only representative of true-false values. In Ruby. nil and false are falsy values, and everything else is a true value. There's no meaning for having
33. In Ruby, true and false are the only representatives
34. As a representative: True: true False: false
35. Other objects: True: 42, 0, “false”, {}, etc. False: nil
36. In Ruby, true and false are the only representatives
37. In Ruby, useful objects have so many methods
38. {}.methods.size # =>
39. 179 (Ruby 3.4.4)
40. ActiveRecord::B ase.instance_me thods.size # =>
41. 402 (Rails 7.1.4)
42. true.methods.siz e # =>
44. Object.new.met hods.size # =>
46. Only 3 unique methods!
47. true.methods - Object.new.met hods # =>
48. [:&, :|, :^]
49. Only logical operators!
50. false.methods == true.methods # =>
51. true
52. Is true almost equal to false because their methods are the same?
53. NO!!!!!!!!!!!!!
54. 
    NFUIPE
    NBUSJY 536& '"-4& 536& 536& '"-4& '"-4& '"-4& '"-4&
55. c
    NFUIPE
    NBUSJY 536& '"-4& 536& 536& 536& '"-4& 536& '"-4&
56. ?
    NFUIPE
    NBUSJY 536& '"-4& 536& '"-4& 536& '"-4& 536& '"-4&
57. Conclusion: true and false share little. They are the only representative, not having useful behaviors.
58. Boolean class
59. Class
60. What is class?
61. > In object-oriented programming, a class de fi nes the shared aspects of objects created from the class. https://en.wikipedia.org/wiki/Class_(computer_programming)
62. Superclass for classes sharing nothing?
63. Rejected for several reasons: many gems and libraries had already introduced Boolean class. I don't want to break them. true and false are the only representative of true- false values. In Ruby. nil and false are falsy values, and everything else is a true value. There's no meaning for having a superclass of TrueClass and FalseClass as Boolean. Matz. ʢUnderscored by the speakerʣ
64. But it should be useful!
65. https://bugs.ruby- lang.org/issues/ 12515
66. Use case: v.is_a?(Boolean)
67. v.is_a?(Boolean) v == true || v == false
68. Rejected for several reasons: many gems and libraries had already introduced Boolean class. I don't want to break them. true and false are the only representative of true-false values. In Ruby. nil and false are falsy values, and everything else is a true value. There's no meaning for having
69. And the compatibility issue
70. Naming is hard • Recently added “Ractor” used to be “Guild” • Game developers complained that they already use “Guild” class • Recently added “Data” class was occupied by Ruby itself so it was safe • Adding “Boolean” may destroy other “Boolean” classes
71. Summary
72. The reasons why we don’t need Boolean class • true and false share nothing • There’s no meaning of a superclass for them • Few use cases • `is_a?(Boolean) might be the only one • Compatibility issues • Naming is hard
73. Lessons learned • Designing a programming language is interesting • In the issue, many developers express their thoughts and ideas • Not always “correct answer” • “This should be useful” might not be a right reason to add something • Ruby is different from other languages
74. Thank you!
75. One More Thing
76. Why doesn't Ruby have Boolean class? RubyConf Tw 2025 OKURA Masafumi ʢେ૔խ࢙ʣ 2025-08-09
78. Matz: Boolean class will be used to check types which I don’t want to encourage
79. Of fi cial™ answer
80. Contact me! • Personal website: https://okuramasafumi.com • ruby.social: https://ruby.social/@okuramasafumi • X: https://x.com/okuramasafumi • GitHub: https://github.com/okuramasafumi • LinkedIn: https://www.linkedin.com/in/masafumi-okura-82651128/