Why doesn't Ruby have Boolean class?

https://2025.rubyconf.tw

Transcript

1. Why doesn't Ruby have Boolean class? RubyConf Tw 2025 OKURA Masafumi ʢେ૔խ࢙ʣ 2025-08-09
2. 㟬޷ʂ
3. Wǒ zài xí zhōngwén! զࡏशதจʂ
4. Wèishéme Ruby méiyǒu bù lín lèi ҝॄኄ Ruby ᔒ༗෍ྛྨ
5. Fāyīn hěn nán! ᚙԻ኷೉ʂ
6. ೉͍͠
7. ͳͥRubyʹ͸BooleanΫϥε ͕ͳ͍ͷ͔ BuriKaigi 2024 OKURA Masafumi, 2024-01-20
8. ͳͥRubyʹ͸BooleanΫϥε ͕ͳ͍ͷ͔ BuriKaigi 2024 OKURA Masafumi, 2024-01-20
9. BuriKaigi
10. Ჳձٞ
11. Ჳ
12. Ჳan
13. Huáng wěi yú 㐋ඌڕ
15. Why doesn't Ruby have Boolean class? RubyConf Tw 2025 OKURA Masafumi ʢେ૔խ࢙ʣ 2025-08-09
16. introduce(self) • Name: OKURA Masafumiʢେ૔խ࢙ɺ͓͓͘Β·͞;Έʣ • 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` • Special note: I’m hosting a table in Code Party this evening!
18. https://rubytaiwan.kktix.cc/events/codeparty2025
22. Why Doesn’t Ruby have Boolean class?
23. 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
24. Takeaways:
25. 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)
26. 1. Fact
27. Demo!
28. 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)
29. 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.)
30. In Ruby, everything is object
31. In Ruby, every object has its Class
32. Singleton classes: TrueClass FalseClass NilClass
33. They exist, but not for practical reasons
34. v.is_a?(TrueClass) v == true
35. 2. Opinion
36. We don’t need Boolean class!
37. https://bugs.ruby-lang.org/issues/12515
38. > Create "Boolean" superclass of TrueClass / FalseClass
39. Status: Rejected
40. 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
41. In Ruby, true and false are the only representatives
42. As a representative: True: true False: false
43. Other objects: True: 42, 0, “false”, {}, etc. False: nil
44. In Ruby, true and false are the only representatives
45. In Ruby, useful objects have so many methods
46. {}.methods.size # =>
47. 179 (Ruby 3.4.4)
48. ActiveRecord::Base.instance_methods.size # =>
49. 402 (Rails 7.1.4)
50. true.methods.size # =>
52. Object.new.methods.size # =>
54. Only 3 unique methods!
55. true.methods - Object.new.methods # =>
56. [:&, :|, :^]
57. Only logical operators!
58. false.methods == true.methods # =>
59. true
60. Is true almost equal to false because their methods are the same?
61. NO!!!!!!!!!!!!!
62. & method matrix TRUE FALSE TRUE TRUE FALSE FALSE FALSE FALSE
63. | method matrix TRUE FALSE TRUE TRUE TRUE FALSE TRUE FALSE
64. ^ method matrix TRUE FALSE TRUE FALSE TRUE FALSE TRUE FALSE
65. Conclusion: true and false share nothing. They are the only representative, not having useful behaviors.
66. Boolean class
67. Class
68. What is class?
69. > In object-oriented programming, a class defines the shared aspects of objects created from the class. https://en.wikipedia.org/wiki/Class_(computer_programming)
70. Superclass for classes sharing nothing?
71. 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
72. But it should be useful!
73. https://bugs.ruby-lang.org/issues/12515
74. Use case: v.is_a?(Boolean)
75. v.is_a?(Boolean) v == true || v == false
76. 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
77. And the compatibility issue
78. 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
79. Summary
80. 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
81. 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
82. Thank you!
83. Find me! • https://okuramasafumi.com • https://bsky.app/profile/okuramasafumi.com • https://ruby.social/@okuramasafumi • https://www.linkedin.com/in/masafumi-okura-82651128/