Write your own Domain Specific Language in Ruby: Let's do some metaprogramming!

- https://tomdebruijn.com/
- https://twitter.com/tombruijn
- https://mastodon.social/@tombruijn

Transcript

1. Write your own DSL in Ruby Let's do some metaprogramming! Tom de Bruijn – mastodon.social/@tombruijn – tomdebruijn.com
2. What is a DSL? ? ? ?
3. Domain Speci fi c Language ? ? ? ? ?
4. A sub-language in Ruby *
 for a Domain A gem, or as part of an app * DSLs can also be made in other languages
5. # Rake example task :hello do puts "Hello there" end
6. $ rake hello Hello there
7. class Profile < TomsSchemaGem plugin LabelPlugin attribute :name, :label => "Name" attribute :socials do label "Social media" attribute :twitter, :label => "Twitter" attribute :mastodon, :label => "Mastodon" end end profile = Profile.new(...) profile.name.label # => "Name" profile.name.value # => "Tom de Bruijn" profile.socials.twitter.value # => "@tombruijn"
8. Why use a DSL?
9. Con fi guration
10. # config/application.rb module MyApp class Application < Rails::Application config.load_defaults 7.0 config.time_zone = "UTC" config.app.custom_option = "foo" end end
11. No YAML required 😌
12. Automate writing code Frameworks provide tools to simplify things
13. Rails.application.routes.draw do resources :posts do resources :comments end root "homepage#show" end
14. Rails.application.routes.draw do resources :posts do resources :comments end root "homepage#show" end resources :posts do resources :comments root "homepage#show"
15. Create routes resources :posts • GET /posts • GET /posts/:id • POST /posts • PUT /posts/:id • DELETE /posts/:id
16. Point to the right controller
17. class User < ApplicationRecord validates :name, :presence => true end
18. Validation validates :name, :presence => true • Validation on creation • Validation on update • Validation on demand • Storing error messages
19. No updating 5 locations for every change
20. Make high churn code more maintainable
21. case ARGV.first when "hello" puts "Hello world" when "bye" puts "Goodbye world" end # ruby tasks.rb hello task :hello do puts "Hello world" end task :bye do puts "Goodbye world" end # rake hello
22. How to write your own DSL?
23. config = Config.new( :verbose => true, :format => :documentation )
24. config = Config.new config.verbose = true config.format = :documentation
25. class Config attr_accessor :verbose, :format end config = Config.new config.verbose = true config.format = :documentation pp config # => #<Config:... @format=:documentation, @verbose=true>
26. class Config attr_accessor :verbose, :format end config = Config.new config.verbose = true config.format = :documentation pp config # => #<Config:... @format=:documentation, @verbose=true> attr_accessor :verbose, :format config.verbose = true config.format = :documentation # => #<Config:... @format=:documentation, @verbose=true>
27. config = Config.new config.verbose = true config.format = :documentation pp config.options # => {:verbose=>true, :format=>:documentation}
28. class Config attr_reader :options def initialize @options = {} end def verbose=(value) @options[:verbose] = value end def format=(value) @options[:format] = value end end
29. class Config attr_reader :options def initialize @options = {} end def verbose(value) @options[:verbose] = value end def format(value) @options[:format] = value end end def verbose=(value) @options[:verbose] = value end def format=(value) @options[:format] = value end
30. New problem: Create methods for every new option def format=(value) @options[:format] = value end def enabled=(value) @options[:enabled] = value end def fail_fast=(value) @options[:fail_fast] = value end def verbose=(value) @options[:verbose] = value end def format=(value) @options[:format] = value end def enabled=(value) @options[:enabled] = value end def fail_fast=(value) @options[:fail_fast] = value end def verbose=(value) @options[:enabled] = value end def fail_fast=(value) @options[:fail_fast] = value end def verbose=(value) @options[:verbose] = value end def format=(value) @options[:format] = value end def enabled=(value) @options[:enabled] = value end def fail_fast=(value) @options[:fail_fast] = value end def verbose=(value) @options[:verbose] = value end def format=(value) @options[:format] = value end def format=(value) @options[:format] = end def enabled=(value) @options[:enabled] end def fail_fast=(value) @options[:fail_fast end def verbose=(value) @options[:verbose] end def format=(value) @options[:format] = end def enabled=(value) @options[:enabled] end def fail_fast=(value) @options[:fail_fast end def verbose=(value) @options[:verbose]
31. Making it more dynamic with ✨ method_missing ✨
32. def method_missing(method_name, *args) [method_name.to_s, *args] end puts welcome to this talk about dsls # welcome # to # this # talk # about # dsls
33. class Config # ... def method_missing(method_name, value) if method_name.end_with? "=" @options[method_name[0..-1]] = value else super # Fall back behavior end end end config = Config.new config.verbose = true config.format = :documentation
34. method_missing may not
 be a good choice
35. What if you call the
 missing method wrong?
36. class Config def method_missing(method_name, value) # ... end end config = Config.new config.verbose # => `method_missing': # wrong number of arguments (given 1, 
 expected 2) (ArgumentError)
37. Unclear where
 methods are de fi ned
38. Breaks respond_to?
39. config = Config.new config.verbose = true pp config.respond_to? :verbose= # => false
40. Dynamically de fi ne
 con fi g option methods
41. class Config def self.def_options(*option_names) option_names.each do |option_name| define_method "#{option_name}=" do |value| options[option_name] = value end end end def_options :verbose, :format # ... end config = Config.new config.verbose = true config.format = :documentation
42. class Config def self.def_options(*option_names) option_names.each do |option_name| define_method "#{option_name}=" do |value| options[option_name] = value end end end def_options :verbose, :format # ... end config = Config.new config.verbose = true config.format = :documentation def_options :verbose, :format
43. class Config def self.def_options(*option_names) option_names.each do |option_name| define_method "#{option_name}=" do |value| options[option_name] = value end end end def_options :verbose, :format # ... end config = Config.new config.verbose = true config.format = :documentation def self.def_options(*option_names) option_names.each do |option_name|
44. class Config def self.def_options(*option_names) option_names.each do |option_name| define_method "#{option_name}=" do |value| options[option_name] = value end end end def_options :verbose, :format # ... end config = Config.new config.verbose = true config.format = :documentation define_method "#{option_name}=" do |value| options[option_name] = value end
45. ⚡ Blocks! ⚡
46. Config.configure do |config| config.verbose = true config.format = :documentation end
47. class Config def self.configure instance = new yield instance instance end # ... end
48. class Config def self.configure instance = new yield instance instance end # ... end def self.configure
49. class Config def self.configure instance = new yield instance instance end # ... end instance = new
50. class Config def self.configure instance = new yield instance instance end # ... end yield instance
51. Config.configure do |config| config.verbose = true config.format = :documentation end |config| config. config.
52. Config.configure do |config| config.verbose = true config.format = :documentation end
53. Config.configure do verbose true format :documentation end
54. class Config def self.configure(&block) instance = new instance.instance_eval(&block) instance end # ... end
55. class Config def self.configure(&block) instance = new instance.instance_eval(&block) instance end # ... end def self.configure(&block)
56. class Config def self.configure(&block) instance = new instance.instance_eval(&block) instance end # ... end instance.instance_eval(&block)
57. Config.configure do verbose true format :documentation end
58. # This won't work! # Ruby will think you're assigning # local variables Config.configure do verbose = true format = :documentation end
59. Config.configure do self.verbose = true self.format = :documentation end self.verbose = self.format =
60. Config.configure do verbose true format :documentation end
61. When to use one or the other?
62. Config.configure do |config| config.verbose = true # Set a value end Config.configure do load_defaults! # Perform an action end
63. # config/puma.rb workers 3 preload_app!
64. Our tools so far •Dynamically de fi ne methods •Ruby blocks
65. Share DSL behavior with modules
66. # Multiple configuration classes Config.configure do enabled true end Output.configure do verbose true format :documentation end
67. class Config include Configurable def_options :enabled end class Output include Configurable def_options :verbose, :format end
68. module Configurable def self.included(base) base.extend ClassMethods end module ClassMethods def def_options(*option_names) # ... end def configure(&block) # ... end end # ...
69. Config.configure do enabled true output do verbose true format :documentation end end
70. class Config include Configurable def_options :enabled class Output include Configurable def_options :verbose, :format end def output(&block) @output ||= Output.new @output.instance_eval(&block) if block_given? @output end end
71. class Config include Configurable def_options :enabled class Output include Configurable def_options :verbose, :format end def output(&block) @output ||= Output.new @output.instance_eval(&block) if block_given? @output end end def output(&block) @output ||= Output.new @output.instance_eval(&block) if block_given? @output end
72. Module builder pattern dejimata.com/2017/5/20/the-ruby-module-builder-pattern
73. class Config include ConfigOption.define(:verbose, :format) end
74. class Config def self.def_options(*option_names) option_names.each do |option_name| define_method option_name do |value| options[option_name] = value end end end def_options :verbose, :format # ... end
75. module ConfigOption def self.define(*option_names) Module.new do def options @options ||= {} end option_names.each do |option_name| define_method option_name do |value| options[option_name] = value end end end
76. module ConfigOption def self.define(*option_names) Module.new do def options @options ||= {} end option_names.each do |option_name| define_method option_name do |value| options[option_name] = value end end end def self.define(*option_names)
77. module ConfigOption def self.define(*option_names) Module.new do def options @options ||= {} end option_names.each do |option_name| define_method option_name do |value| options[option_name] = value end end end define_method option_name do |value| options[option_name] = value end
78. module ConfigOption def self.define(*option_names) Module.new do def options @options ||= {} end option_names.each do |option_name| define_method option_name do |value| options[option_name] = value end end end Module.new do end
79. class Config include ConfigOption.define(:verbose, :format) end
80. Advantage:
 Easy to reuse everywhere
81. Advantage:
 No con fi g option de fi nition logic in the class itself
82. # Anonymous module pp Config.included_modules # => [#<Module:...>, Kernel]
83. class Config include ConfigOption.new(:verbose, :format) end
84. class Config include ConfigOption.new(:verbose, :format) end new
85. class ConfigOption < Module def initialize(*option_names) define_method :options do @options ||= {} end option_names.each do |option_name| define_method option_name do |value| options[option_name] = value end end
86. class ConfigOption < Module def initialize(*option_names) define_method :options do @options ||= {} end option_names.each do |option_name| define_method option_name do |value| options[option_name] = value end end class ConfigOption < Module
87. class ConfigOption < Module def initialize(*option_names) define_method :options do @options ||= {} end option_names.each do |option_name| define_method option_name do |value| options[option_name] = value end end def initialize(*option_names)
88. class ConfigOption < Module def initialize(*option_names) define_method :options do @options ||= {} end option_names.each do |option_name| define_method option_name do |value| options[option_name] = value end end define_method :options do @options ||= {} end define_method option_name do |value| options[option_name] = value end
89. # Anonymous module pp Config.included_modules # => [#<Module:...>, Kernel] # Named module pp Config.included_modules # => [#<ConfigOption:...>, Kernel]
90. Read this post: dejimata.com/2017/5/20/the-ruby-module-builder-pattern
91. Create DSL objects Keep the DSL and created object separate
92. class Config def self.configure(&block) dsl = ConfigDSL.dsl(&block) new(dsl.options) end # ... end Config.configure do verbose true format :documentation end class ConfigDSL include ConfigOption.new( :verbose, :format) def self.dsl(&block) instance = new instance .instance_eval(&block) instance end end
93. class Config def self.configure(&block) dsl = ConfigDSL.dsl(&block) new(dsl.options) end # ... end Config.configure do verbose true format :documentation end class ConfigDSL include ConfigOption.new( :verbose, :format) def self.dsl(&block) instance = new instance .instance_eval(&block) instance end end dsl = ConfigDSL.dsl(&block) new(dsl.options) class ConfigDSL def self.dsl(&block)
94. Make small modules, like plugins Small modules are easier to maintain than very large classes
95. class Profile < TomsSchemaGem plugin LabelPlugin attribute :name, :label => "Name" attribute :socials do label "Social media" attribute :twitter, :label => "Twitter" attribute :mastodon, :label => "Mastodon" end end profile = Profile.new(...) profile.name.label # => "Name" profile.name.value # => "Tom de Bruijn" profile.socials.twitter.value # => "@tombruijn"
96. class Profile < TomsSchemaGem plugin LabelPlugin attribute :name, :label => "Name" attribute :socials do label "Social media" attribute :twitter, :label => "Twitter" attribute :mastodon, :label => "Mastodon" end end profile = Profile.new(...) profile.name.label # => "Name" profile.name.value # => "Tom de Bruijn" profile.socials.twitter.value # => "@tombruijn" plugin LabelPlugin label "Social media" profile.name.label # => "Name"
97. class Profile < TomsSchemaGem plugin LabelPlugin attribute :name, :label => "Name" attribute :socials do label "Social media" profile.name.label # => "Name" plugin LabelPlugin :label => "Name" label "Social media" profile.name.label # => "Name"
98. module LabelPlugin < PluginDSL option :label attribute_method :label do options[:label] end end
99. In summary • method_missing • de fi ne_method • Ruby blocks • yield • instance_eval • Modules • share behavior between classes • Module builder pattern • DSL objects - move DSL logic to separate classes • Create plugins
100. Now go forth and make your DSL!
101. Thank you! Do something nice for someone that’s not yourself. Join a union. DSL DS DSL Tom de Bruijn – mastodon.social/@tombruijn – tomdebruijn.com