The document discusses Ruby metaprogramming techniques such as class variables, class inheritance, singleton classes, blocks, evaluation, dynamic method definition, mixins, monkey patching, and hooks. It provides examples of how these techniques can be combined to add dynamic behavior to classes and modules in Ruby.

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