1. RUBY META
PROGRAMMING.

2. @fnando

3. AVISOS.

4. TUDO É OBJETO.
INCLUINDO CLASSES.

5. MUITO CÓDIGO.

6. VARIÁVEIS DE
CLASSE.

7. class MyLib
@@name = "mylib"
def self.name
@@name
end
end

8. MyLib.name
#=> “mylib”

9. class MyOtherLib < MyLib
@@name = "myotherlib"
end

10. MyOtherLib.name
#=> “myotherlib”
MyLib.name
#=> “myotherlib”

11. VARIÁVEIS DE
CLASSE SÃO
COMPARTILHADAS.

12. VARIÁVEIS DE
INSTÂNCIA.

13. class MyLib
@name = "mylib"
def self.name
@name
end
end

14. MyLib.name
#=> “mylib”

15. class MyOtherLib < MyLib
@name = "myotherlib"
end

16. MyOtherLib.name
#=> “myotherlib”
MyLib.name
#=> “mylib”

17. VARIÁVEIS DE
INSTÂNCIA
PERTENCEM
AO OBJETO.

18. METACLASSE.

19. class MyLib
class << self
end
end

20. class MyLib # ruby 1.9.2+
singleton_class.class_eval do
end
end

21. class Object
def singleton_class
class << self; self; end
end
end unless Object.respond_to?(:singleton_class)

22. class MyLib
class << self
attr_accessor :name
end
end

23. MyLib.name = "mylib"
MyLib.name
#=> mylib

24. BLOCOS.

25. MÉTODOS PODEM
RECEBER BLOCOS.

26. def run(&block)
end

27. BLOCOS PODEM
SER EXECUTADOS.

28. def run(&block)
yield arg1, arg2
end

29. def run(&block)
block.call(arg1, arg2)
end

30. def run(&block)
block[arg1, arg2]
end

31. def run(&block) # ruby 1.9+
block.(arg1, arg2)
end

32. METACLASSE,
BLOCOS E
VARIÁVEL DE
INSTÂNCIA.

33. MyLib.configure do |config|
config.name = "mylib"
end

34. class MyLib
class << self
attr_accessor :name
end
def self.configure(&block)
yield self
end
end

35. EVALUATION.

36. eval, class_eval, e
instance_eval

37. MyLib.class_eval <<-RUBY
"running inside class"
RUBY
#=> “running inside class”

38. MyLib.class_eval do
"running inside class"
end
#=> “running inside class”

39. handler = proc {
self.kind_of?(MyLib)
}
handler.call
#=> false

40. handler = proc {
self.kind_of?(MyLib)
}
lib.instance_eval(&handler)
#=> true

41. BLOCOS,
METACLASSE,
VARIÁVEIS DE
INSTÂNCIA,
EVALUATION.

42. MyLib.configure do
self.name = "mylib"
name
#=> “mylib”
end

43. class MyLib
class << self
attr_accessor :name
end
def self.configure(&block)
instance_eval(&block)
end
end

44. DEFINIÇÃO DE
MÉTODOS.

45. MONKEY
PATCHING.

46. class Integer
def kbytes
self * 1024
end
end
128.kbytes
#=> 131072

47. define_method.

48. MyLib.class_eval do
define_method "name" do
@name
end
define_method "name=" do |name|
@name = name
end
end

49. lib = MyLib.new
lib.name = "mynewname"
lib.name
#=> “mynewname”

50. EVALUATION.

51. MyLib.class_eval <<-RUBY
def self.name
"mylib"
end
def name
"mylib's instance"
end
RUBY

52. MyLib.class_eval do
def self.name
"mylib"
end
def name
"mylib's instance"
end
end

53. MyLib.name
#=> “mylib”
MyLib.new.name
#=> “mylib’s instance”

54. BLOCOS,
EVALUATION,
DEFINIÇÃO DE
MÉTODOS.

55. MyLib.class_eval do
name "mylib"
name
#=> “mylib”
end

56. class MyLib
def self.accessor(method)
class_eval <<-RUBY
def self.#{method}(*args)
if args.size.zero?
@#{method}
else
@#{method} = args.last
end
end
RUBY
end
accessor :name
end

57. MyLib.class_eval do
name "mylib"
name
#=> “mylib”
end

58. configure do
name "mylib"
name
#=> “mylib”
end

59. def configure(&block)
MyLib.instance_eval(&block)
end

60. DISCLAIMER.

61. METHOD MISSING.

62. MyLib.new.invalid

63. NoMethodError: undefined method ‘invalid’ for
#<MyLib:0x10017e2f0>

64. class MyLib
NAMES = { :name => "mylib’s instance" }
def method_missing(method, *args)
if NAMES.key?(method.to_sym)
NAMES[method.to_sym]
else
super
end
end
end

65. class MyLib
#...
def respond_to?(method, include_private = false)
if NAMES.key?(method.to_sym)
true
else
super
end
end
end

66. lib.name
#=> “mylib’s instance”
lib.respond_to?(:name)
#=> true

67. MIXINS.

68. class MyLib
extend Accessor
accessor :name
end
class MyOtherLib
extend Accessor
accessor :name
end

69. module Accessor
def accessor(name)
class_eval <<-RUBY
def self.#{name}(*args)
if args.size.zero?
@#{name}
else
@#{name} = args.last
end
end
RUBY
end
end

70. MONKEY
PATCHING, MIXINS,
EVALUATION,
DYNAMIC
DISPATCHING E
HOOKS.

71. class Conference < ActiveRecord::Base
has_permalink
end

72. "welcome to QConSP".to_permalink
#=> “welcome-to-qconsqp”

73. class String
def to_permalink
self.downcase.gsub(/[^[a-z0-9]-]/, "-")
end
end

74. class Conference < ActiveRecord::Base
before_validation :generate_permalink
def generate_permalink
write_attribute :permalink, name.to_s.to_permalink
end
end

75. module Permalink
end
ActiveRecord::Base.send :include, Permalink

76. module Permalink
def self.included(base)
base.send :extend, ClassMethods
end
end

77. module Permalink
# ...
module ClassMethods
def has_permalink
class_eval do
before_validation :generate_permalink
include InstanceMethods
end
end
end
end

78. module Permalink
# ...
module InstanceMethods
def generate_permalink
write_attribute :permalink, name.to_s.to_permalink
end
end
end

79. conf = Conference.create(:name => "QConSP 2010")
conf.permalink
#=> "qconsp-2010"

80. ENTÃO...

81. META
PROGRAMMING É
COMPLICADO.

82. MAS NEM TANTO.

83. APRENDA RUBY.

84. OBRIGADO.

85. nandovieira.com.br
simplesideias.com.br
spesa.com.br
github.com/fnando
@fnando