Ruby Metaprogramming

Transcript

1. Ruby Metaprogramming Sergio Gil (@porras)

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3. require 'excel' require 'sql' Excel.load('file.xls').each do |row| SQL.insert(row) end

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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

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9. Metaprogramming

10. defining metaprogramming

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15. Classes Instances Methods Variables Constants Modules

16. Classes Instances Methods Variables Constants Modules

17. Memory

18. Classes Instances Methods Variables Constants Modules

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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

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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
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39. It’s all about expresivity

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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

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54. “Cleverness cannot win. The only weapons we have are simplicity

    and convention” http://alarmingdevelopment.org/?p=422

55. Thank you :)