This document provides an overview of metaprogramming in Ruby. It discusses writing programs that write programs, also known as metaprogramming, which is commonly used in Ruby through methods like attr_accessor. The document discusses why metaprogramming is useful and some common Ruby techniques for metaprogramming like class_eval, instance_eval, and method_missing. It also covers topics like scoping, method dispatch, defining methods, and intercepting method calls through method_missing.

1. Metaprogramming
in Ruby

2. Things I Wish I Knew
When I Started Ruby

5. Who?
Joshua Hull
@jj
https://github.com/joshbuddy

6. What?

7. What?
Writing programs that write programs.

8. What?
Writing programs that write programs.
NOT code generation!

9. Why?
We all do it.

10. Why?
We all do it.
Ruby attr_accessor :my_attribute

11. Why?
We all do it.
Ruby attr_accessor :my_attribute
def my_attribute
@my_attribute
end
def my_attribute=(my_attribute)
@my_attribute = my_attribute
end

12. Why?
We all do it.
Ruby attr_accessor :my_attribute
Java public int getAttribute() {
return attribute;
}
public void setAttribute(int newAttribute) {
attribute = newAttribute;
}

13. Why?
We all do it.
ner
in Ruby
W attr_accessor :my_attribute
Java public int getAttribute() {
return attribute;
}
public void setAttribute(int newAttribute) {
attribute = newAttribute;
}

14. Why?
def age
@age || 'not set'
end
def gender
@gender || 'not set'
end
def name
@name || 'not set'
end

15. Why?
def age
@age || 'not set'
end
def gender
@gender || 'not set'
end
def name
@name || 'not set'
end
[:age, :gender, :name].each do |attr|
define_method(attr) do
instance_variable_get(:"@#{attr}") || 'not set'
end
end

16. Drawbacks

17. Drawbacks
You can write some difficult-to-understand code.

18. Drawbacks
You can write some difficult-to-understand code.

19. Method dispatch

20. Method dispatch
class MyObject
attr_accessor :name
def say_hello
puts "hello"
puts name
end
end

21. Method dispatch
class MyObject
attr_accessor :name
def say_hello
puts "hello"
puts name
end
end This is a
method call,
but who receives it?

22. Method dispatch
class MyObject
attr_accessor :name
def say_hello
puts "hello"
puts self.name
end
end

23. Method dispatch
class MyObject
attr_accessor :name
def say_hello
puts "hello"
puts self.name
end
end
self is always the
implied receiver!

24. Method dispatch
class MyObject
attr_accessor :name
def say_hello
puts "hello"
puts name
end
end

25. Method dispatch
class MyObject
self.attr_accessor :name
def say_hello
puts "hello"
puts name
end
end

26. Method dispatch
class MyObject
Who is self self.attr_accessor :name
here? def say_hello
puts "hello"
puts name
end
end

27. Method dispatch
class MyObject
Who is self self.attr_accessor :name
here? def say_hello
puts "hello"
The class puts name
end
is! end

28. Method dispatch
Module#attr
Who is self
here?
The class
is!

29. Ruby classes

30. Ruby classes
class NewClass
def hey
puts 'hello!'
end
end

31. Ruby classes
class NewClass
{
def hey
puts 'hello!'
end
end
This is normal
code!

32. Ruby classes
class NewClass
def hey
puts 'hello!'
end
end
is the same as
NewClass = Class.new do
def hey
puts 'hello!'
end
end

33. Ruby classes
class ParsingError < RuntimeError
end

34. Ruby classes
class ParsingError < RuntimeError
end
is the same as
ParsingError = Class.new(RuntimeError)

35. Ruby classes
def class_with_accessors(*attributes)
Class.new do
attr_accessor *attributes
end
end

36. Ruby classes
def class_with_accessors(*attributes)
Class.new do
attr_accessor *attributes
end
end
Returns a new class!

37. Ruby classes
def class_with_accessors(*attributes)
Class.new do
attr_accessor *attributes
end
end
Returns a new class!
class Person < class_with_accessors(:name, :age, :sex)
# ...
end

38. eval, instance_eval,
class_eval

39. eval, instance_eval,
class_eval
Method
eval
instance_eval
class_eval

40. eval, instance_eval,
class_eval
Method Context
eval your current context
instance_eval the object
class_eval the object’s class

41. eval, instance_eval,
class_eval
eval
eval "puts 'hello'"
# hello

42. eval, instance_eval,
class_eval
instance_eval
class MyClass
end
MyClass.instance_eval("def hi; 'hi'; end")

43. eval, instance_eval,
class_eval
instance_eval
class MyClass
end
MyClass.instance_eval("def hi; 'hi'; end")
MyClass.hi
# 'hi'

44. eval, instance_eval,
class_eval
instance_eval
class MyClass
end
MyClass.instance_eval("def hi; 'hi' end")
obj = MyClass.new
# <MyClass:0x10178aff8>
obj.hi
# NoMethodError: undefined method `hi' for #<MyClass>

45. eval, instance_eval,
class_eval
class_eval
class MyClass
end
MyClass.class_eval("def hi; 'hi' end")

46. eval, instance_eval,
class_eval
class_eval
class MyClass
end
MyClass.class_eval("def hi; 'hi' end")
MyClass.hi
# NoMethodError: undefined method `hi' for MyClass:Class

47. eval, instance_eval,
class_eval
class_eval
class MyClass
end
MyClass.class_eval("def hi; 'hi' end")
obj = MyClass.new
# <MyClass:0x101849688>
obj.hi
# "hi"

48. eval, instance_eval,
class_eval
class_eval instance_eval
class MyClass class MyClass
end end
MyClass.class_eval("def hi; 'hi'; end") MyClass.instance_eval("def hi; 'hi'; end")
obj = MyClass.new MyClass.hi
# <MyClass:0x101849688> # 'hi'
obj.hi
# "hi"

49. eval, instance_eval,
class_eval
Ninja’s will attack you if ...
you don’t use __FILE__, __LINE__

50. eval, instance_eval,
class_eval
class HiThere
end
HiThere.class_eval "def hi; raise; end"
HiThere.class_eval "def hi_with_niceness; raise; end", __FILE__, __LINE__
HiThere.new.hi
HiThere.new.hi_with_niceness

51. eval, instance_eval,
class_eval
class HiThere
end
HiThere.class_eval "def hi; raise; end"
HiThere.class_eval "def hi_with_niceness; raise; end", __FILE__, __LINE__
HiThere.new.hi
HiThere.new.hi_with_niceness
(eval):1:in `hi': unhandled exception
from my_file.rb:7
my_file.rb:5:in `hi_with_niceness': unhandled exception
from my_file.rb:7

52. eval, instance_eval,
class_eval
class HiThere
end
HiThere.class_eval "def hi; raise; end"
HiThere.class_eval "def hi_with_niceness; raise; end", __FILE__, __LINE__
HiThere.new.hi
HiThere.new.hi_with_niceness
(eval):1:in `hi': unhandled exception
from my_file.rb:7
So nice. <3
my_file.rb:5:in `hi_with_niceness': unhandled exception
from my_file.rb:7

53. eval, instance_eval,
class_eval
Implement attr_accessor!

54. eval, instance_eval,
class_eval
class Module
def create_attr(attribute)
class_eval("def #{attribute}; @#{attribute}; end")
end
end

55. eval, instance_eval,
class_eval
class Module
def create_attr(attribute)
class_eval("def #{attribute}; @#{attribute}; end")
end
end
class M
create_attr :hi
end

56. eval, instance_eval,
class_eval
class Module
def create_attr(attribute)
class_eval("def #{attribute}; @#{attribute}; end")
end
end
def M
class M def hi
create_attr :hi @hi
end end
end

57. Defining methods

58. Defining methods
For an object
o = Object.new
o.instance_eval("def just_this_object; end")
o.just_this_object

59. Defining methods
For an object
o = Object.new
o.instance_eval("def just_this_object; end")
o.just_this_object
Object.new.just_this_object
# NoMethodError: undefined method `just_this_object'

60. Defining methods
For an object
o = Object.new
o.instance_eval("def just_this_object; end")
o.just_this_object
Object.new.just_this_object
# NoMethodError: undefined method `just_this_object'
o = Object.new
o.instance_eval {
def just_this_object
end
}

61. Defining methods
For an object
o = Object.new
o.extend(Module.new {
def just_this_object
end
})

62. Defining methods
For a class
MyClass = Class.new
class MyClass
def new_method
end
end
MyClass.new.respond_to?(:new_method) # true

63. Defining methods
For a class
MyClass = Class.new
MyClass.class_eval " MyClass.class_eval do
def new_method def new_method
end end
" end
MyClass.send(:define_method, :new_method) {
# your method body
}

64. Defining methods
Aliasing
Module#alias_method

65. Scoping

66. Scoping
module Project
class Main
def run
# ...
end
end
end

67. Scoping
module Project
class Main
def run
# ...
end
end
end
Class definitions
Module definitions
Method definitions

68. Scoping
a = 'hello'
module Project
class Main
def run
puts a
end
end
end
Project::Main.new.run

69. Scoping
a = 'hello'
module Project
class Main
def run
puts a
end
end
end
Project::Main.new.run
# undefined local variable or method `a' for #<Project::Main> (NameError)

70. Scoping
module Project
class Main
end
end
a = 'hello'
Project::Main.class_eval do
define_method(:run) do
puts a
end
end
Project::Main.new.run # => hello

71. Scoping
Example: Connection Sharing
module AddConnections
def self.add_connection_methods(cls, host, port)
cls.class_eval do
define_method(:get_connection) do
puts "Getting connection for #{host}:#{port}"
end
define_method(:host) { host }
define_method(:port) { port }
end
end
end

72. Scoping
Example: Connection Sharing
module AddConnections
def self.add_connection_methods(cls, host, port)
cls.class_eval do
define_method(:get_connection) do
puts "Getting connection for #{host}:#{port}"
end
define_method(:host) { host }
define_method(:port) { port }
end
end
end
Client = Class.new
AddConnections.add_connection_methods(Client, 'localhost', 8080)
Client.new.get_connection # Getting connection for localhost:8080
Client.new.host # localhost
Client.new.port # 8080

73. Scoping
Kernel#binding
Let’s you leak the current “bindings”

74. Scoping
Kernel#binding
Let’s you leak the current “bindings”
def create_connection(bind)
eval '
connection = "I am a connection"
', bind
end
connection = nil
create_connection(binding)
connection # => I am a connection

75. Scoping
Kernel#binding
Let’s you leak the current “bindings”
def create_connection(bind)
eval '
connection = "I am a connection"
', bind
end
Calls connection = nil
with the create_connection(binding)
current connection # => I am a connection
state

76. Scoping
Kernel#binding
Let’s you leak the current “bindings”
def create_connection(bind)
eval '
connection = "I am a connection"
', bind
end
Calls connection = nil
with the create_connection(binding)
current connection # => I am a connection
state
MAGIC!

77. Scoping
Kernel#binding
Let’s you leak the current “bindings”
def create_connection(bind)
eval '
connection = "I am a connection"
', bind
end
# connection = nil
create_connection(binding)
connection
# undefined local variable or method `connection'

78. Scoping
Kernel#binding
Let’s you leak the current “bindings”
def create_connection(bind)
eval '
connection = "I am a connection"
', bind
end
# connection = nil
create_connection(binding)
connection
# undefined local variable or method `connection'
You can’t add to the local variables via binding

79. Scoping
Kernel#binding
Let’s you leak the current “bindings”
def create_connection(bind)
eval '
connection = "I am a connection"
', bind
end
eval "connection = nil"
create_connection(binding)
connection
# undefined local variable or method `connection'
You can’t add to the local variables via eval

80. Scoping
Kernel#binding
TOPLEVEL_BINDING

81. Scoping
Kernel#binding
TOPLEVEL_BINDING
a = 'hello'
module Program
class Main
def run
puts eval("a", TOPLEVEL_BINDING)
end
end
end
Program::Main.new.run # => hello

82. Interception!
(aka lazy magic)

83. Interception!
method_missing(method, *args, &blk)

84. Interception!
method_missing(method, *args, &blk)
class MethodMissing
def method_missing(m, *args, &blk)
puts "method_missing #{m} #{args.inspect} #{blk.inspect}"
super
end
end

85. Interception!
method_missing(method, *args, &blk)
class MethodMissing
def method_missing(m, *args, &blk)
puts "method_missing #{m} #{args.inspect} #{blk.inspect}"
super
end
end
mm = MethodMissing.new
mm.i_dont_know_this(1, 2, 3)
# method_missing i_dont_know_this [1, 2, 3] nil
# NoMethodError: undefined method `i_dont_know_this' for #<MethodMissing>

86. Interception!
Example: Timing
module MethodsWithTiming
def method_missing(m, *args, &blk)
if timed_method = m.to_s[/^(.*)_with_timing$/, 1] and respond_to?(timed_method)
respond = nil
measurement = Benchmark.measure {
respond = send(timed_method, *args, &blk)
}
puts "Method #{m} took #{measurement}"
respond
else
super
end
end
end

87. Interception!
Example: Timing
module MethodsWithTiming
def method_missing(m, *args, &blk)
if timed_method = m.to_s[/^(.*)_with_timing$/, 1] and respond_to?(timed_method)
respond = nil
measurement = Benchmark.measure {
respond = send(timed_method, *args, &blk)
}
puts "Method #{m} took #{measurement}"
respond
else
super
end
end
end
sc = SlowClass.new
class SlowClass
sc.slow
include MethodsWithTiming
def slow
sleep 1
sc.slow_with_timing
end
# Method slow_with_timing took 0.000000 0.000000 0.000000 ( 1.000088)
end

88. Interception!
Example: Proxy
class Proxy
def initialize(backing)
@backing = backing
end
def method_missing(m, *args, &blk)
@backing.send(m, *args, &blk)
end
end

89. Interception!
Example: Proxy
class LoggingProxy
def initialize(backing)
@backing = backing
end
def method_missing(m, *args, &blk)
puts "Calling method #{m} with #{args.inspect}"
@backing.send(m, *args, &blk)
end
end

90. Interception!
Example: Simple DSL
class NameCollector
attr_reader :names
def initialize
@names = []
end
def method_missing(method, *args, &blk)
args.empty? ? @names.push(method.to_s.capitalize) : super
end
end
nc = NameCollector.new
nc.josh
nc.bob
nc.jane
nc.names.join(' ') # => Josh Bob Jane

91. Interception!
Object#respond_to?(sym)

92. Interception!
Object#respond_to?(sym)
Example: Timing
module MethodsWithTiming
alias_method :original_respond_to?, :respond_to?
def method_missing(m, *args, &blk)
if timed_method = m.to_s[/^(.*)_with_timing$/, 1] and original_respond_to?(timed_method)
respond = nil
measurement = Benchmark.measure {
respond = send(timed_method, *args, &blk)
}
puts "Method #{m} took #{measurement}"
respond
else
super
end
end
def respond_to?(sym)
(timed_method = sym.to_s[/^(.*)_with_timing$/, 1]) ?
original_respond_to?(timed_method.to_sym) :
original_respond_to?(sym)
end
end

93. Interception!
Object#respond_to?(sym)
Example: Timing
module MethodsWithTiming
ge ts
alias_method :original_respond_to?, :respond_to?
It
def method_missing(m, *args, &blk)
r!
if timed_method = m.to_s[/^(.*)_with_timing$/, 1] and original_respond_to?(timed_method)
te
respond = nil
et
measurement = Benchmark.measure {
b
respond = send(timed_method, *args, &blk)
}
puts "Method #{m} took #{measurement}"
respond
else
super
end
end
def respond_to?(sym)
(timed_method = sym.to_s[/^(.*)_with_timing$/, 1]) ?
original_respond_to?(timed_method.to_sym) :
original_respond_to?(sym)
end
end

94. Interception!
Object#respond_to_missing?(sym) (1.9 only)
Example: Timing
module MethodsWithTiming
def method_missing(m, *args, &blk)
if timed_method = m.to_s[/^(.*)_with_timing$/, 1] and respond_to?(timed_method)
respond = nil
measurement = Benchmark.measure {
respond = send(timed_method, *args, &blk)
}
puts "Method #{m} took #{measurement}"
respond
else
super
end
end
def respond_to_missing?(sym)
(timed_method = sym.to_s[/^(.*)_with_timing$/, 1]) ?
respond_to?(timed_method.to_sym) :
super
end
end

95. Interception!
const_missing(sym)

96. Interception!
const_missing(sym)
MyClass::MyOtherClass
# MyClass.const_missing(:MyOtherClass)

97. Interception!
const_missing(sym)
MyClass::MyOtherClass
# MyClass.const_missing(:MyOtherClass)
Example: Loader
class Loader
def self.const_missing(sym)
file = File.join(File.dirname(__FILE__), "#{sym.to_s.downcase}.rb")
if File.exist?(file)
require file
Object.const_defined?(sym) ? Object.const_get(sym) : super
else
puts "can't find #{file}, sorry!"
super
end
end
end

98. Interception!
Example: Loader
class Loader
def self.const_missing(sym)
file = File.join(File.dirname(__FILE__), "#{sym.to_s.downcase}.rb")
if File.exist?(file)
require file
Object.const_defined?(sym) ? Object.const_get(sym) : super
else
puts "can't find #{file}, sorry!"
super
end
end
end

99. Interception!
Example: Loader
class Loader
def self.const_missing(sym)
file = File.join(File.dirname(__FILE__), "#{sym.to_s.downcase}.rb")
if File.exist?(file)
require file
Object.const_defined?(sym) ? Object.const_get(sym) : super
else
puts "can't find #{file}, sorry!"
super
end
end
end
Loader::Auto
# can't find ./auto.rb, sorry!
# NameError: uninitialized constant Loader::Auto
# or, if you have an ./auto.rb
Loader::Auto
# => Auto

100. Callbacks

101. Callbacks
Module#method_added

102. Callbacks
Module#method_added

103. Callbacks
Module#method_added
class MyClass
def self.method_added(m)
puts "adding #{m}"
end
puts "defining my method"
def my_method
'two'
end
puts "done defining my method"
end

104. Callbacks
Module#method_added
class MyClass defining my method
def self.method_added(m) adding my_method
puts "adding #{m}" done defining my method
end
puts "defining my method"
def my_method
'two'
end
puts "done defining my method"
end

105. Callbacks
Module#method_added
Example: Thor!
class Tasks
def self.desc(desc)
@desc = desc
end
def self.method_added(m)
(@method_descs ||= {})[m] = @desc
@desc = nil
end
def self.method_description(m)
method_defined?(m) ?
@method_descs[m] || "This action isn't documented" :
"This action doesn't exist"
end
desc "Start server"
def start
end
def stop
end
end

106. Callbacks
Module#method_added
Example: Thor! Record the description
class Tasks
def self.desc(desc)
@desc = desc
When a method is added,
end record the description associated
def self.method_added(m) with that method
(@method_descs ||= {})[m] = @desc
@desc = nil
end Provide the description for a
def self.method_description(m)
method, or, if not found, some
method_defined?(m) ? default string.
@method_descs[m] || "This action isn't documented" :
"This action doesn't exist"
end
desc "Start server"
def start
end
def stop
end
end

107. Callbacks
Module#method_added
Example: Thor! Record the description
class Tasks
def self.desc(desc)
@desc = desc
When a method is added,
end record the description associated
def self.method_added(m) with that method
(@method_descs ||= {})[m] = @desc
@desc = nil
end Provide the description for a
def self.method_description(m)
method, or, if not found, some
method_defined?(m) ? default string.
@method_descs[m] || "This action isn't documented" :
"This action doesn't exist"
end
desc "Start server"
def start
end
Described!
def stop
end
end

108. Callbacks
Module#method_added
Example: Thor! Query your methods!
class Tasks puts Tasks.method_description(:start)
def self.desc(desc) # => Start server
@desc = desc puts Tasks.method_description(:stop)
end
# => This action isn't documented
def self.method_added(m) puts Tasks.method_description(:restart)
(@method_descs ||= {})[m] = @desc # => This action doesn't exist
@desc = nil
end
def self.method_description(m)
method_defined?(m) ?
@method_descs[m] || "This action isn't documented" :
"This action doesn't exist"
end
desc "Start server"
def start
end
def stop
end
end

109. Callbacks
Object#singleton_method_added

110. Callbacks
Object#singleton_method_added
class ClassWithMethods
def self.singleton_method_added(m)
puts "ADDING! #{m}"
end
def self.another
end
end

111. Callbacks
Object#singleton_method_added
class ClassWithMethods
def self.singleton_method_added(m)
puts "ADDING! #{m}"
end
def self.another
end
end
# ADDING! singleton_method_added
# ADDING! another

112. Callbacks
Object#singleton_method_added
class ClassWithMethods
def self.singleton_method_added(m)
puts "ADDING! #{m}"
end
def self.another
end
end
Holy meta!
# ADDING! singleton_method_added
# ADDING! another

113. Callbacks
Module#included
module Logger
def self.included(m)
puts "adding logging to #{m}"
end
end
class Server
include Logger
end
# adding logging to Server

114. Callbacks
Module#included
Example: ClassMethods pattern
module Logger class Server
def self.included(m) include Logger
puts "adding logging to #{m}"
end def self.create
log("Creating server!")
def self.log(message) end
puts "LOG: #{message}" end
end
end
Server.create
# `create': undefined method `log' for Server:Class (NoMethodError)

115. Callbacks
Module#included
Example: ClassMethods pattern
module Logger class Server
def self.included(m) include Logger
m.extend(ClassMethods)
end def self.create
log("Creating server!")
module ClassMethods end
def log(message) end
puts "LOG: #{message}"
end
end
end
Server.create
# LOG: Creating server!

116. Callbacks
Module#extended
module One
def self.extended(obj)
puts "#{self} has been extended by #{obj}"
end
end
Object.new.extend(One)
# One has been extended by #<Object:0x1019614a8>

117. Callbacks
Class#inherited
class Parent
def self.inherited(o)
puts "#{self} was inherited by #{o}"
end
end
class Child < Parent
end
# Parent was inherited by Child

118. Callbacks
Guarding callbacks
Module#append_features include
Module#extend_object extend
def self.extend_object(o)
super
end
def self.append_features(o)
super
end

119. Callbacks
Guarding callbacks
Module#append_features include
Module#extend_object extend
def self.append_features(o)
o.instance_method(:<=>) ? super : warn('you no can uze')
end

120. Callbacks
Kernel#caller
def one
two
end
def two
method name
three
file name line (optional)
end
def three
p caller
end
# ["method.rb:156:in `two'", "method.rb:152:in `one'", "method.rb:163"]
https://github.com/joshbuddy/callsite

121. Callbacks
Module#nesting
module A
module B
module C
p Module.nesting
end
end
end
# [A::B::C, A::B, A]

122. There and back again, a
parsing tale

123. There and back again, a
parsing tale
gem install ruby_parser
gem install sexp_processor
gem install ruby2ruby
Let’s go!

124. There and back again, a
parsing tale
Parsing
require 'rubygems'
require 'ruby_parser'
RubyParser.new.process("'string'")
s(:str, "string")
Type Arguments...

125. There and back again, a
parsing tale
Parsing
require 'rubygems'
require 'ruby_parser'
RubyParser.new.process("'string'")
s(:str, "string")
[:str, "string"] # Sexp
Sexp.superclass
# Array

126. There and back again, a
parsing tale
Parsing
RubyParser.new.process("'string' + 'string'")
s(:call, s(:str, "string"), :+, s(:arglist, s(:str, "string")))
Method Method
Receiver Arguments
call name

127. There and back again, a
parsing tale
Parsing
RubyParser.new.process("'string' + 'string'")
s(:call, nil, :puts, s(:arglist, s(:str, "hello world")))
Method Receiver Method
Arguments
call name

128. There and back again, a
parsing tale
And, back again...
require 'rubygems'
require 'ruby2ruby'
Ruby2Ruby.new.process [:str, "hello"] # => "hello"

129. There and back again, a
parsing tale
And, back again...
require 'rubygems'
require 'ruby2ruby'
Ruby2Ruby.new.process [:str, "hello"] # => "hello"
Ruby2Ruby.new.process [:lit, :symbol] # => :symbol

130. There and back again, a
parsing tale
Roundtrip
require 'sexp_processor'
require 'ruby2ruby'
require 'ruby_parser'
class JarJarify < SexpProcessor
def initialize
self.strict = false
super
end
def process_str(str)
new_string = "YOUZA GONNA SAY #{str[-1]}"
str.clear
s(:str, new_string)
end
end

131. There and back again, a
parsing tale
Roundtrip
class JarJarify < SexpProcessor
def initialize
self.strict = false
super
end
def process_str(str)
new_string = "YOUZA GONNA SAY #{str[-1]}"
str.clear
s(:str, new_string)
end
end
ast = RubyParser.new.process('puts "hello"')
Ruby2Ruby.new.process(JarJarify.new.process(ast))
# => puts("YOUZA GONNA SAY hello")

132. There and back again, a
parsing tale
Roundtrip
class JarJarify < SexpProcessor
def initialize
self.strict = false
Process type :str
super
end
def process_str(str)
new_string = "YOUZA GONNA SAY #{str[-1]}"
str.clear
s(:str, new_string) Consume the current sexp
end
end Return a new one
ast = RubyParser.new.process('puts "hello"')
Ruby2Ruby.new.process(JarJarify.new.process(ast))
# => puts("YOUZA GONNA SAY hello")

133. IT’S OVER!