Module Magic

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

Transcript

1. MODULE MAGIC
   and my trip to RubyKaigi2009
   

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2. JAMES EDWARD
   GRAY II
   

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

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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
   

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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
   

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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/
   

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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
   

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8. LSRC SPEECHES
   TV shows geeks should know!
   

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9. LSRC SPEECHES
   TV shows geeks should know!
   

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10. RUBYKAIGI2009
    

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11. RUBYKAIGI2009
    

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12. RUBYKAIGI2009
    See how the Japanese do
    conferences
    

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

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

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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!
    

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28. MIXIN MODULES
    

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

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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
    

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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!
    

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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
    

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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
    

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39. INHERITANCE
    p E.ancestors
    

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

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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
    

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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
    

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

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

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

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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
    

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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
    

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54. JUST A SHORTCUT
    We now know what extend() really is
    

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55. JUST A SHORTCUT
    We now know what extend() really is
    obj.extend(Mod)
    

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56. JUST A SHORTCUT
    We now know what extend() really is
    obj.extend(Mod)
    class << obj
    include Mod
    end
    

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57. NAMESPACE
    MODULES
    

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

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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
    

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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
    

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

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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
    

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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
    

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

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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
    

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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
    

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75. LIMITED MAGIC
    Summon new error types as needed
    

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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
    

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77. SOME EXAMPLES
    Bridging the theory to implementation gap
    

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78. SOME EXAMPLES
    Bridging the theory to implementation gap
    

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

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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
    

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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
    # ...
    

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

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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)
    

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

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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
    

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

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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
    

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96. OBJECT EDITING
    Using hooks to edit objects
    

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

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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
    

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99. SUMMARY
    

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100. SUMMARY
     

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

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

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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
     

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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()
     

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105. QUESTIONS?
     

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