I gave this speech at LSRC 2009 to explain the fundamentals of Ruby's method look-up system.

1. MODULE MAGIC
and my trip to RubyKaigi2009

2. JAMES EDWARD
GRAY II

3. JAMES EDWARD
GRAY II
Created the Ruby Quiz and wrote that book

4. JAMES EDWARD
GRAY II
Created the Ruby Quiz and wrote that book
Built FasterCSV (now CSV), HighLine (with Greg), Elif, and
some other scarier experiments

5. JAMES EDWARD
GRAY II
Created the Ruby Quiz and wrote that book
Built FasterCSV (now CSV), HighLine (with Greg), Elif, and
some other scarier experiments
Documented some of Ruby

6. JAMES EDWARD
GRAY II
Created the Ruby Quiz and wrote that book
Built FasterCSV (now CSV), HighLine (with Greg), Elif, and
some other scarier experiments
Documented some of Ruby
http://blog.grayproductions.net/

7. JAMES EDWARD
GRAY II
Created the Ruby Quiz and wrote that book
Built FasterCSV (now CSV), HighLine (with Greg), Elif, and
some other scarier experiments
Documented some of Ruby
http://blog.grayproductions.net/
http://twitter.com/JEG2

8. LSRC SPEECHES
TV shows geeks should know!

9. LSRC SPEECHES
TV shows geeks should know!

10. RUBYKAIGI2009

11. RUBYKAIGI2009

12. RUBYKAIGI2009
See how the Japanese do
conferences

13. RUBYKAIGI2009
See how the Japanese do
conferences
The translation time
allows you to think more

14. RUBYKAIGI2009
See how the Japanese do
conferences
The translation time
allows you to think more
Meet nice Rubyists from
Japan and other places

15. RUBYKAIGI2009
See how the Japanese do
conferences
The translation time
allows you to think more
Meet nice Rubyists from
Japan and other places
See Japan!

29. MIXIN MODULES

30. A TRIVIAL MIXIN
I’m sure most of us know this

31. module Mixin
def shared_method
puts "Called!"
end
end
class Whatever
include Mixin
end
Whatever.new.shared_method
A TRIVIAL MIXIN
I’m sure most of us know this

32. module Mixin
def shared_method
puts "Called!"
end
end
class Whatever
Called!
include Mixin
end
Whatever.new.shared_method
A TRIVIAL MIXIN
I’m sure most of us know this

38. class A
def call
puts "A"
end
end
%w[B C D].each do |name|
eval <<-END_RUBY
module #{name}
def call
puts "#{name}"
super
end
end
END_RUBY
end
class E < A
include B
include C
include D
def call
puts "E"
super
end
end
E.new.call

39. E
class A
def call
puts "A"
end
end
D
%w[B C D].each do |name|
eval <<-END_RUBY
module #{name}
def call
puts "#{name}"
super
C
end
end
END_RUBY
end
B
class E < A
include B
include C
include D
def call
puts "E"
A
super
end
end
E.new.call

40. INHERITANCE
p E.ancestors

41. [E, D, C, B, A, Object, Kernel, BasicObject]
INHERITANCE
p E.ancestors

47. class A
def call
puts "A"
end
end
%w[B C D].each do |name|
eval <<-END_RUBY
module #{name}
def call
puts "#{name}"
super
end
end
END_RUBY
end
a = A.new
a.extend(B)
a.extend(C)
a.extend(D)
a.call

48. D
class A
def call
puts "A"
end
end
C
%w[B C D].each do |name|
eval <<-END_RUBY
module #{name}
def call
puts "#{name}"
super
B
end
end
END_RUBY
end
A
a = A.new
a.extend(B)
a.extend(C)
a.extend(D)
a.call

49. INVISIBLE CLASS
class << a; p ancestors end

50. [D, C, B, A, Object, Kernel, BasicObject]
INVISIBLE CLASS
class << a; p ancestors end

51. The (invisible) “singleton class” is here
[D, C, B, A, Object, Kernel, BasicObject]
INVISIBLE CLASS
class << a; p ancestors end

53. class A
def call
puts "A"
end
end
%w[B C D].each do |name|
eval <<-END_RUBY
module #{name}
def call
puts "#{name}"
super
end
end
END_RUBY
end
a = A.new
a.extend(B)
a.extend(C)
a.extend(D)
class << a
def call
puts "Invisible"
super
end
end
a.call

54. class A
def call
puts "A"
end
Invisible
end
%w[B C D].each do |name|
eval <<-END_RUBY
D
module #{name}
def call
puts "#{name}"
super
C
end
end
END_RUBY
end
B
a = A.new
a.extend(B)
a.extend(C)
a.extend(D)
A
class << a
def call
puts "Invisible"
super
end
end
a.call

55. JUST A SHORTCUT
We now know what extend() rea#y is

56. obj.extend(Mod)
JUST A SHORTCUT
We now know what extend() rea#y is

57. class << obj
obj.extend(Mod) include Mod
end
JUST A SHORTCUT
We now know what extend() rea#y is

59. NAMESPACE
MODULES

60. GROUP CONSTANTS
Group constants/classes and even mix them in

61. class Logger
# ...
# Logging severity.
module Severity
DEBUG = 0
INFO = 1
WARN = 2
ERROR = 3
FATAL = 4
UNKNOWN = 5
end
include Severity
# ...
end
GROUP CONSTANTS
Group constants/classes and even mix them in

62. class Logger module JSON
# ...
# Logging severity. class Array
module Severity
DEBUG = 0
# ...
INFO = 1 end
WARN = 2
ERROR = 3 class Object
FATAL = 4
UNKNOWN = 5
# ...
end end
include Severity
# ... # ...
end end
GROUP CONSTANTS
Group constants/classes and even mix them in

67. DUAL INTERFACE
Some modules are both a namespace and a mixin

68. module MoreMath
def self.dist(x1, y1, x2, y2)
Math.sqrt( (x2 - x1) ** 2 +
(y2 - y1) ** 2 )
end
end
DUAL INTERFACE
Some modules are both a namespace and a mixin

69. module MoreMath module MoreMath
def self.dist(x1, y1, x2, y2) extend Math
def self.dist( x1, y1,
Math.sqrt( (x2 - x1) ** 2 + x2, y2 )
(y2 - y1) ** 2 ) sqrt( (x2 - x1) ** 2 +
(y2 - y1) ** 2 )
end end
end
end
DUAL INTERFACE
Some modules are both a namespace and a mixin

70. MIXIN YOURSELF
Better than Ruby’s module_function()

71. module MiniLogger
extend self
def logger
$stdout
end
def log(message)
logger.puts "%s: %s" %
[ Time.now.strftime("%D %H:%M:%S"),
message ]
end
end
if __FILE__ == $PROGRAM_NAME
MiniLogger.log "Called as a module method and " +
"written to $stdout."
end
MIXIN YOURSELF
Better than Ruby’s module_function()

72. module MiniLogger require "mini_logger"
extend self
def logger class Whatever
$stdout include MiniLogger
end def logger
def log(message) @logger ||=
open("whatever.log", "w")
logger.puts "%s: %s" %
end
[ Time.now.strftime("%D %H:%M:%S"),
def initialize
message ]
log "Called as an " +
end "instance method " +
end "and written to " +
"a file."
if __FILE__ == $PROGRAM_NAME end
MiniLogger.log "Called as a module method and " + end
"written to $stdout."
end Whatever.new
MIXIN YOURSELF
Better than Ruby’s module_function()

77. LIMITED MAGIC
Summon new error types as needed

78. module Errors
class BaseError < RuntimeError; end
def self.const_missing(error_name)
if error_name.to_s =~ /wErrorz/
const_set(error_name, Class.new(BaseError))
else
super
end
end
end
p Errors::SaveError
LIMITED MAGIC
Summon new error types as needed

79. SOME EXAMPLES
Bridging the theory to implementation gap

80. SOME EXAMPLES
Bridging the theory to implementation gap

81. A BIT TOO CLEVER
If RDoc can’t read it, it’s probably too clever

82. require "ostruct"
class << Config = OpenStruct.new
def update_from_config_file(path = config_file)
eval <<-END_UPDATE
config = self
#{File.read(path)}
config
END_UPDATE
end
# ...
end
Config.config_file = "config.rb"
Config.update_from_config_file
A BIT TOO CLEVER
If RDoc can’t read it, it’s probably too clever

83. require "ostruct"
class << Config = OpenStruct.new
def update_from_config_file(path = config_file)
eval <<-END_UPDATE
config = self
#{File.read(path)} config.command = "ls"
config config.retries = 42
END_UPDATE # ...
end
# ...
end
Config.config_file = "config.rb"
Config.update_from_config_file
A BIT TOO CLEVER
If RDoc can’t read it, it’s probably too clever

84. LESS MAGIC
RDoc and I can both read it now

85. require "ostruct"
# These extra methods are mixed into the OpenStruct stored in Config.
module Configured
# This method loads configuration settings from a plain Ruby file.
def update_from_config_file(path = config_file)
eval <<-END_UPDATE
config = self
#{File.read(path)}
config
END_UPDATE
end
# ...
end
# This constant holds all global configuration, see Configured for details.
Config = OpenStruct.new.extend(Configured)
LESS MAGIC
RDoc and I can both read it now

90. WITH CLASS METHODS
A classic pattern made popular by Rails

91. module DoubleMixin
module ClassMethods
# ...
end
module InstanceMethods
# ...
end
def self.included(receiver)
receiver.extend(ClassMethods)
receiver.send(:include, InstanceMethods)
end
end
WITH CLASS METHODS
A classic pattern made popular by Rails

96. LABELING OBJECTS
You can use a do-nothing module as a type

97. module DRb
# ...
module DRbUndumped
def _dump(dummy) # :nodoc:
raise TypeError, 'can't dump'
end
end
# ...
class DRbMessage
# ...
def dump(obj, error=false) # :nodoc:
obj = make_proxy(obj, error) if obj.kind_of? DRbUndumped
# ...
end
# ...
end
# ...
end
LABELING OBJECTS
You can use a do-nothing module as a type

98. OBJECT EDITING
Using hooks to edit objects

99. p "ruby".strip!.
capitalize!
# NoMethodError:
# undefined method
# `capitalize!' for
# nil:NilClass
OBJECT EDITING
Using hooks to edit objects

100. module SafelyChainable
def self.extended(singleton)
singleton.methods.grep(/w!z/).
each do |bang|
p "ruby".strip!. singleton.instance_eval <<-END_RUBY
def #{bang}
capitalize!
super
self
# NoMethodError:
end
# undefined method END_RUBY
# `capitalize!' for end
# nil:NilClass end
end
p "ruby".extend(SafelyChainable).
strip!.capitalize!
OBJECT EDITING
Using hooks to edit objects

101. SUMMARY

102. SUMMARY

103. SUMMARY
Master Ruby’s method
lookup; it’s worth the effort

104. SUMMARY
Master Ruby’s method
lookup; it’s worth the effort
Modules are a terrific at
limiting the scope of magic

105. SUMMARY
Master Ruby’s method
lookup; it’s worth the effort
Modules are a terrific at
limiting the scope of magic
Remember, modules can
modify individual objects

106. SUMMARY
Master Ruby’s method
lookup; it’s worth the effort
Modules are a terrific at
limiting the scope of magic
Remember, modules can
modify individual objects
Try replacing some
inheritance with extend()

108. QUESTIONS?