Slides of my talk in RubyKaigi 2010 on DSLs.

1. The Basis of Making DSL
with Ruby
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2. Who I am
• Yasuko Ohba
• Ruby Programmer
• Developing rails applications
and iPhone applications
• Everyleaf Corporation
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3. Housekeeping Book on Web
Kozuchi
• http://www.kozuchi.net
• http://github.com/everyleaf/kozuchi
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4. • @nay3 (twitter)
• http://github.com/nay
• y.ohba@everyleaf.com
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5. 2010 8 28

6. 2010 8 28

7. 2010 8 28

8. 2010 8 28

9. 2010 8 28

10. 2010 8 28

11. 2010 8 28

12. Ruby is good for
DSL
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13. Domain Specific
Language
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14. DSL
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15. DSL
Hospitals
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16. Libraries
DSL
Hospitals
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17. Libraries Game
DSL
Hospitals
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18. Libraries Game
DSL
Hospitals EC
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19. It looks like a
language rather than a
program
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20. DSL
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21. internal
DSL
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22. external
internal
DSL
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23. internal DSL
in Ruby
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24. DSL examples
• Rails
• routes.rb
• migrations
• RJS
• RSpec
• Rake
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25. DSL-like codes : Rails
class NotesController
before_filter :find_group
...
end
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26. before_filter :find_group
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27. It doesn’t
look like DSL ?
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28. it can be less DSL like
self.add_before_filter_methods(
:find_group)
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29. much more DSL like
self.add_before_filter_methods(
:find_group)
before_filter :find_group
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30. My talk is simple
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31. I’ll talk about
readable codes
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32. DSL-like codes : migrations
create_table :users do |t|
t.string :name
t.timestamps
end
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33. DSL-like codes : RSpec
describe Group do
it “name ” do
g = Group.new
g.should_not be_valid
end
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34. Easy to read
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35. Easy to write
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36. Brief
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37. Easy to maintain
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38. OK, but...
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39. Do we just use
existing great DSLs ?
Photo by Lawrence OP
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40. NO
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41. Write your ruby
codes like DSL
everyday
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42. That’s just a skill of
programming in Ruby
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43. I’m going to talk
about
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44. ..how to make your
codes like DSL
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45. Our goal
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46. DSL-likeness
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47. What decides
whether it is DSL
or not ?
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48. No Solid Boundary
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49. But we can feel it
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50. to make the
difference clear
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51. Compare normal
Ruby codes and DSLs
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52. Normal Ruby Style
“Hey receiver, do/return THIS !”
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53. Hey receiver do THIS!
array.clear
array[1]
array.collect!{...}
hash.delete(key)
string.empty?
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54. Because it’s OOP
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55. DSLs have
another styles
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56. 3 typical forms
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57. 1.Declarative Programming
2.Using Blocks
3.Methods Represent Special
Concepts
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58. 1. Declarative
Programming
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59. “I am a rubyist”
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60. examples : declarative expression
validates_presence_of :name
before_filter ...
has_many :children
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61. typical features
• describe status or nature
• receivers are not always important
• no brackets
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62. No money
self.money = 0
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63. No money
self.money = 0
poor
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64. Mostly in Class
Definitions
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65. No money
class Boy
poor
...
end
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66. Try to express your
request as a nature
of the class
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67. Object task
task
task
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68. the class has this nature
Object task
task
task
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69. Modules are good
to express natures
Class Object
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70. Modules are good
to express natures
Class Object
Module
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71. Modules are good
to express natures
Class Object
Module Module
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72. implementation
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73. Example 1
Declare the class to have
some nature implemented as
a module
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74. Book
(Class)
class Book
include "Product"
...
end
Product
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75. class Book
include "Product"
...
end
class Book
acts_as_product
...
end
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76. class Book
acts_as_product
...
end
NameError: undefined local variable or
method `acts_as_product' for Book:Class
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77. You need
acts_as_product
method
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78. in the super class
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79. Book Object
(Class) (Class)
acts_as_product
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80. Book Object
(Class) (Class)
acts_as_product
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81. Book Object
(Class) (Class)
acts_as_product
Product
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82. the easier way
class Object
def self.acts_as_product
include Product
end
end
the caller (Book) will be self here
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83. Book
(Class)
class Book
acts_as_product
...
end
Product
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84. class Object
def self.acts_as_product
include Product
end
end
Execute this before acts_as_product is invoked
Rails config/initializer/acts_as_product.rb
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85. the softer way
module ActsAsProduct
module ClassMethods
def acts_as_product
include Product
end
end
def self.included(base)
base.extend(ClassMethods)
end
end
Object.instance_eval { include ActsAsProduct }
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86. Object
(Class)
ActsAsProduct
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87. Object
(Class)
add
ActsAsProduct acts_as_product
ClassMethods
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88. Book Object
(Class) (Class)
add
ActsAsProduct acts_as_product
ClassMethods
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89. Book Object
(Class) (Class)
call
acts_as_product
add
ActsAsProduct acts_as_product
ClassMethods
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90. Book Object
(Class) (Class)
call
acts_as_product
add
ActsAsProduct acts_as_product
Product
ClassMethods
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91. Example 2
set @title for a layout in some
actions in Rails controllers
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92. Request
Controller
index show new edit
@title
layout
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93. want to write like this
class BooksController < ApplicationController
title " ", :only => [:edit, :update]
....
end
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94. Same Strategy
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95. add a class method
in the super class
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96. ApplicationController
title
BooksController
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97. ApplicationController
class ApplicationController < ...
def self.title
...
end
end
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98. title " ",
:only => [:edit, :update]
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99. ApplicationController
class ApplicationController < ...
attr_accessor :title
def self.title(name, options={})
before_filter(options) {|controller|
controller.title = name}
end
.....
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100. English naming
problems
validate ?
validates ?
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101. 2. Using Blocks
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102. examples : rake
namespace :myapp do
task :my_rake_task do
# rake
end
end
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103. Example : Rails Form
Helper
form_for :book do |f|
f.text_field :name
f.submit
end
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104. Usages of block for DSL
• describe complex structure
• get some tasks into a scope
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105. describe structure
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106. Example 3
Write a game rule
using playing cards
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107. Sevens
game 'sevens' do |g|
g.use 53
g.deal 53, :to => :each_player
...
end
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108. Top
You Level
Game
game use
deal
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109. class Game
def use (card_size, options ={})
...
end
def deal (card_size, options ={})
...
end
end
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110. def game
g = Game.new
yield g
end
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111. Top Game
You Level
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112. Top Game
You Level
game
Block
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113. Top Game
You Level
game new
Block
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114. Top Game
You Level
game new
Block
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115. Top Game
You Level
use
game new
deal
Block
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116. want the block
parameter removed?
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117. without parameter g
game 'sevens' do
use 53
deal 53, :to => :each_player
...
end
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118. use instance_exec
def game(&block)
g = Game.new
g.instance_exec(&block)
end
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119. can be changed slightly
game 'sevens' do
uses 53
deals 53, :to => :each_player
...
end
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120. 3. methods represent
special concepts
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121. methods
that work as noun
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122. methods that represent
vocabularies
in another language
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123. books_url
f.submit page.assert
session request
current_user
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124. an extra DSL style
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125. 4. Methods to make
codes like English
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126. should
it years_since
bytes
from_now
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127. Balance
REALLY Cosmos
Useful ? of OOP
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128. General Tips
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129. General Tips
• provide default values for parameters
• use a hash parameter
• use symbols
• naming methods nicely
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130. Summary
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131. DSL is
not very special
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132. Implementation will
improve with DSL ideas
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133. Have a try !
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134. The best way to learn
is reading codes
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135. Thank you !
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