Ruby Metaprogramming

Slides from my talk at #codemotion #es (Madrid, March 24th 2012).

http://codemotion.es/

Transcript

1. Ruby Metaprogramming Sergio Gil (@porras)
3. require 'excel' require 'sql' Excel.load('file.xls').each do |row| SQL.insert(row) end
5. require 'html' require 'http' page = HTML.load(HTTP.get('http://example.com/')) page.links.each do |link| HTTP.get(link).save end
6. class Company def projects HTTP::Request.new('/projects').get end def people HTTP::Request.new('/people').get end def clients HTTP::Request.new('/clients').get end ... end
7. Yukihiro Matsumoto ‘Matz’, Ruby creator
9. Metaprogramming
10. defining metaprogramming
15. Classes Instances Methods Variables Constants Modules
16. Classes Instances Methods Variables Constants Modules
17. Memory
18. Classes Instances Methods Variables Constants Modules
20. >> str = "hola" => "hola"
21. >> str = "hola" => "hola" >> str.methods => [..., :reverse, ...]
22. >> str = "hola" => "hola" >> str.methods => [..., :reverse, ...] >> def str.reverse "adios" end
23. >> str = "hola" => "hola" >> str.methods => [..., :reverse, ...] >> def str.reverse "adios" end >> str.reverse
24. >> str = "hola" => "hola" >> str.methods => [..., :reverse, ...] >> def str.reverse "adios" end >> str.reverse => "adios"
25. Ruby Object Model: The Musical
31. It’s all about DRYness
32. class Company def projects HTTP::Request.new('/projects').get end def people HTTP::Request.new('/people').get end ... end
33. class Company def projects get('/projects') end def people get('/people') end ... private def get(url) HTTP::Request.new(url).get end end
34. Is that all?
35. Let Ruby create your methods for you
36. class Company [:projects, :people, ...].each do |method| eval %Q{ def #{method} HTTP::Request.new('/#{method}').get end } end end
37. class Company [:projects, :people, ...].each do |method| define_method method do HTTP::Request.new("/#{method}").get end end end
39. It’s all about expresivity
41. module HTTP def get(*methods) methods.each do |method| define_method method do HTTP::Request.new("/#{method}").get end end end end
42. module HTTP def get(*methods) methods.each do |method| define_method method do HTTP::Request.new("/#{method}").get end end end end class Company extend HTTP get :projects, :people, ... end
43. “I Taw a Putty DSL...”
44. class Company extend HTTP get :projects, :people, ... end
45. It’s all about flexibility
46. class Company def method_missing(method, *args, &blk) HTTP::Request.new("/#{method}").get end end
47. class Company def method_missing(method, *args, &blk) HTTP::Request.new("/#{method}").get end end
48. It’s all common sense
49. metaprogramming == programming
50. same trade-offs apply
54. “Cleverness cannot win. The only weapons we have are simplicity and convention” http://alarmingdevelopment.org/?p=422
55. Thank you :)