Module Magic

A deep dive into how Ruby's modules really fit into the language.

Transcript

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!
28. MIXIN MODULES
29. A TRIVIAL MIXIN I’m sure most of us know this
30. A TRIVIAL MIXIN I’m sure most of us know this module Mixin def shared_method puts "Called!" end end ! class Whatever include Mixin end ! Whatever.new.shared_method
31. A TRIVIAL MIXIN I’m sure most of us know this module Mixin def shared_method puts "Called!" end end ! class Whatever include Mixin end ! Whatever.new.shared_method Called!
37. 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
38. E D C B A 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. INHERITANCE p E.ancestors
40. INHERITANCE p E.ancestors [E, D, C, B, A, Object, Kernel, BasicObject]
46. 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
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 D C B A
48. INVISIBLE CLASS class << a; p ancestors end
49. INVISIBLE CLASS class << a; p ancestors end [D, C, B, A, Object, Kernel, BasicObject]
50. INVISIBLE CLASS class << a; p ancestors end [D, C, B, A, Object, Kernel, BasicObject] The (invisible) “singleton class” is here
52. 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
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 Invisible D C B A
54. JUST A SHORTCUT We now know what extend() really is
55. JUST A SHORTCUT We now know what extend() really is obj.extend(Mod)
56. JUST A SHORTCUT We now know what extend() really is obj.extend(Mod) class << obj include Mod end
57. NAMESPACE MODULES
58. GROUP CONSTANTS Group constants/classes and even mix them in
59. GROUP CONSTANTS Group constants/classes and even mix them in class Logger # ... # Logging severity. module Severity DEBUG = 0 INFO = 1 WARN = 2 ERROR = 3 FATAL = 4 UNKNOWN = 5 end include Severity # ... end
60. GROUP CONSTANTS Group constants/classes and even mix them in class Logger # ... # Logging severity. module Severity DEBUG = 0 INFO = 1 WARN = 2 ERROR = 3 FATAL = 4 UNKNOWN = 5 end include Severity # ... end module JSON class Array # ... end class Object # ... end # ... end
65. DUAL INTERFACE Some modules are both a namespace and a mixin
66. DUAL INTERFACE Some modules are both a namespace and a mixin module MoreMath def self.dist(x1, y1, x2, y2) Math.sqrt( (x2 - x1) ** 2 + (y2 - y1) ** 2 ) end end
67. DUAL INTERFACE Some modules are both a namespace and a mixin module MoreMath def self.dist(x1, y1, x2, y2) Math.sqrt( (x2 - x1) ** 2 + (y2 - y1) ** 2 ) end end module MoreMath extend Math def self.dist( x1, y1, x2, y2 ) sqrt( (x2 - x1) ** 2 + (y2 - y1) ** 2 ) end end
68. MIXIN YOURSELF Better than Ruby’s module_function()
69. MIXIN YOURSELF Better than Ruby’s module_function() 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
70. MIXIN YOURSELF Better than Ruby’s module_function() require "mini_logger" ! class Whatever include MiniLogger def logger @logger ||= open("whatever.log", "w") end def initialize log "Called as an " + "instance method " + "and written to " + "a file." end end ! Whatever.new 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
75. LIMITED MAGIC Summon new error types as needed
76. LIMITED MAGIC Summon new error types as needed module Errors class BaseError < RuntimeError; end def self.const_missing(error_name) if error_name.to_s =~ /\wError\z/ const_set(error_name, Class.new(BaseError)) else super end end end ! p Errors::SaveError
77. SOME EXAMPLES Bridging the theory to implementation gap
78. SOME EXAMPLES Bridging the theory to implementation gap
79. A BIT TOO CLEVER If RDoc can’t read it, it’s probably too clever
80. A BIT TOO CLEVER If RDoc can’t read it, it’s probably too clever 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
81. A BIT TOO CLEVER If RDoc can’t read it, it’s probably too clever 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 config.command = "ls" config.retries = 42 # ...
82. LESS MAGIC RDoc and I can both read it now
83. LESS MAGIC RDoc and I can both read it now 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)
88. WITH CLASS METHODS A classic pattern made popular by Rails
89. WITH CLASS METHODS A classic pattern made popular by Rails module DoubleMixin module ClassMethods # ... end module InstanceMethods # ... end def self.included(receiver) receiver.extend(ClassMethods) receiver.send(:include, InstanceMethods) end end
94. LABELING OBJECTS You can use a do-nothing module as a type
95. LABELING OBJECTS You can use a do-nothing module as a type 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
96. OBJECT EDITING Using hooks to edit objects
97. OBJECT EDITING Using hooks to edit objects p "ruby".strip!. capitalize! ! # NoMethodError: # undefined method # `capitalize!' for # nil:NilClass
98. OBJECT EDITING Using hooks to edit objects module SafelyChainable def self.extended(singleton) singleton.methods.grep(/\w!\z/). each do |bang| singleton.instance_eval <<-END_RUBY def #{bang} super self end END_RUBY end end end ! p "ruby".extend(SafelyChainable). strip!.capitalize! p "ruby".strip!. capitalize! ! # NoMethodError: # undefined method # `capitalize!' for # nil:NilClass
99. SUMMARY
100. SUMMARY
101. SUMMARY Master Ruby’s method lookup; it’s worth the effort
102. SUMMARY Master Ruby’s method lookup; it’s worth the effort Modules are a terrific at limiting the scope of magic
103. 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
104. 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()
105. QUESTIONS?