Metaprogramming isn't real, it can't hurt you

https://rubyconfth.com

1. Metaprogramming isn't real, it can't hurt you RubyConf Th 2026 OKURA Masafumi, 2026-02-01
2. ส วั ส ดี ค รั บ
3. “Metaprogramming"
5. “isn’t real, it can’t hurt you”
7. Skull Cow
8. Metaprogramming is like a Skull Cow * Citation needed
9. It actually does NOT exist, but some people fear it
11. Therapist
12. Me
13. me.introduce(self) • Name: Masa, OKURA Masafumi (Masafumi is the given name) • Job: Freelance web developer • Activities: Kaigi on Rails founder, Ruby community organizer, public speaker, OSS programmer (Alba is the most famous one) • Status: Job opportunities are welcome!
14. https://www. fl ickr.com/photos/143951935@N07/28350408591 CC BY-SA 2.0
15. Japan, a “different” country
16. A “home” country for Ruby
17. Two Japanese speakers
18. Kaigi on Rails
20. 2026-10-16,17
21. Speaker note: I need to talk about T-shirt
23. Alba
25. v3.10.0 was released at 2025-11-11
26. v1.0.0 was released at 2021-04-07
27. 40 months
28. git log v1.0.0..v3.10.0 --oneline | wc -l
30. https://www. fl ickr.com/photos/edyson/13832022/
31. Agenda 1. Introduction to metaprogramming 2. Metaprogramming usage and evolution in real world: Alba as an example 3. Lessons and thoughts 4. Conclusion: Metaprogramming isn’t real, it can’t hurt you
32. 1. Introduction to metaprogramming
33. What is metaprogramming?
34. “Metaprogramming is a computer programming technique in which computer programs have the ability to treat other programs as their data.” https://en.wikipedia.org/wiki/Metaprogramming
38. “Metaprogramming is writing code that writes code” Metaprogramming Ruby
40. Some examples of metaprogramming in Ruby • Module#de fi ne_method • A method that de fi nes a method • Kernel#eval • A method that treats strings as Ruby code • Object#send • A method that treats an argument as a method name
41. More subtle examples • Hook methods such as Class#inherited and BasicObject#method_missing • It does something when Ruby does important things • Scope change such as BasicObject#instance_eval • It mimics as if the current self is that object • Class.new • A method that returns a new class that is de fi ned dynamically
42. Some much more complex examples • Re fi nements • It modi fi es existing classes only in current fi le • TracePoint • It does something when Ruby does… things (even new line) • Binding • It returns a “binding”, which includes things such as current local variables
43. 2. Metaprogramming usage and evolution in real world: Alba as an example
44. Conditional Attributes
46. Performance and error-prune code
47. 3. Lessons and thoughts
48. I used some techniques to make my code better
49. That was somehow called metaprogramming
50. Techniques used in Alba (referenced from the book) • Class Extension • Class Instance Variable • Class Macro • Deferred Evaluation • Dynamic Dispatch • Dynamic Method • Hook Method • String of Code
51. I didn’t do metaprogramming because it’s cool
52. I didn’t do metaprogramming because it’s beautiful
53. I didn’t do metaprogramming because it’s elegant
54. I did metaprogramming because I needed to
55. Before writing code, I knew what Alba should offer
57. Interface ↑ Metaprogramming
58. When should we use metaprogramming?
60. When should we use metaprogramming? • When we need it and we cannot solve the problem otherwise • When we understand what we are doing well • When the components with metaprogramming is well encapsulated and isolated from other parts of the code
61. When should we use metaprogramming? • When we need and it cannot solve the problem otherwise • KISS (Keep It Simple, Stupid) • When we understand what we are doing well • Of course :) • When the components with metaprogramming is well encapsulated and isolated from other parts of the code • Basic OOP principle
62. … Anything special here?
63. “But it hurts me!” A Rubyist
64. When we should NOT use metaprogramming • When you don’t have enough knowledge about how Ruby works • Read “Metaprogramming Ruby” book fi rst! • When you work on something you don’t understand well enough • It tends to be over-engineering • When you work on something that must be stable • Stable interfaces must hide metaprogramming back
65. 4. Conclusion
66. “There’s no such thing as metaprogramming” Metaprogramming Ruby
67. “Programming is real, metaprogramming isn’t. Enjoy programming!” Masafumi Okura
68. ขอบ คุ ณค รั บ
69. 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/