$

rails new myapp $

create create README.md create Rakefile create .ruby-version create config.ru create .gitignore create .gitattributes create Gemfile run git init from "." ... create tmp $ rails new myapp $

(myapp) $

bin/rails generate model User name:string role:string (myapp) $

invoke active_record create db/migrate/20120909070000_create_users.rb create app/models/user.rb (myapp) $ bin/rails generate model User name:string role:string (myapp) $

invoke active_record create db/migrate/20120909070000_create_users.rb create app/models/user.rb (myapp) $ bat app/models/user.rb bin/rails generate model User name:string role:string (myapp) $

invoke active_record create db/migrate/20120909070000_create_users.rb create app/models/user.rb (myapp) $ bat app/models/user.rb bin/rails generate model User name:string role:string (myapp) $ ───────┬────────────────────────────────────────────────────────────────────── │ File: app/models/user.rb ───────┼────────────────────────────────────────────────────────────────────── 1 │ class User < ApplicationRecord 2 │ end ───────┴──────────────────────────────────────────────────────────────────────

invoke active_record create db/migrate/20120909070000_create_users.rb create app/models/user.rb (myapp) $ bat app/models/user.rb bin/rails generate model User name:string role:string (myapp) $ ───────┬────────────────────────────────────────────────────────────────────── │ File: app/models/user.rb ───────┼────────────────────────────────────────────────────────────────────── 1 │ class User < ApplicationRecord 2 │ end ───────┴────────────────────────────────────────────────────────────────────── 🤔

Demystifying DSLs for better analysis and understanding Ufuk Kayserilioglu @paracycle

What is a DSL anyway?

Domain Speci fi c Language

Uses Ruby metaprogramming

Gemfile

Rakefile

RSpec tests

Rails!

So what's so cool about them?

No boilerplate

Natural API

Great, how can I build one?

class CreditCard include Encryptable attr_encrypted :number end

module Encryptable def self.included(mod) mod.extend(ClassMethods) end module ClassMethods def attr_encrypted(attr_name) attr_accessor(attr_name) encrypted_attr_name = "#{attr_name}_encrypted" define_method(encrypted_attr_name) do value = send(attr_name) encrypt(value) end define_method("#{encrypted_attr_name}=") do |value| send("#{attr_name}=", decrypt(value)) end end end private def encrypt(value) value.unpack("H*").first end def decrypt(value) [value].pack("H*") end end

module Encryptable def self.included(mod) mod.extend(ClassMethods) end module ClassMethods def attr_encrypted(attr_name) attr_accessor(attr_name) encrypted_attr_name = "#{attr_name}_encrypted" define_method(encrypted_attr_name) do value = send(attr_name) encrypt(value) end define_method("#{encrypted_attr_name}=") do |value| send("#{attr_name}=", decrypt(value)) end end end private def encrypt(value) value.unpack("H*").first end def decrypt(value) [value].pack("H*") end end

module Encryptable def self.included(mod) mod.extend(ClassMethods) end module ClassMethods def attr_encrypted(attr_name) attr_accessor(attr_name) encrypted_attr_name = "#{attr_name}_encrypted" define_method(encrypted_attr_name) do value = send(attr_name) encrypt(value) end define_method("#{encrypted_attr_name}=") do |value| send("#{attr_name}=", decrypt(value)) end end end private def encrypt(value) value.unpack("H*").first end def decrypt(value) [value].pack("H*") end end

module Encryptable def self.included(mod) mod.extend(ClassMethods) end module ClassMethods def attr_encrypted(attr_name) attr_accessor(attr_name) encrypted_attr_name = "#{attr_name}_encrypted" define_method(encrypted_attr_name) do value = send(attr_name) encrypt(value) end define_method("#{encrypted_attr_name}=") do |value| send("#{attr_name}=", decrypt(value)) end end end private def encrypt(value) value.unpack("H*").first end def decrypt(value) [value].pack("H*") end end

module Encryptable def self.included(mod) mod.extend(ClassMethods) end module ClassMethods def attr_encrypted(attr_name) attr_accessor(attr_name) encrypted_attr_name = "#{attr_name}_encrypted" define_method(encrypted_attr_name) do value = send(attr_name) encrypt(value) end define_method("#{encrypted_attr_name}=") do |value| send("#{attr_name}=", decrypt(value)) end end end private def encrypt(value) value.unpack("H*").first end def decrypt(value) [value].pack("H*") end end

module Encryptable def self.included(mod) mod.extend(ClassMethods) end module ClassMethods def attr_encrypted(attr_name) attr_accessor(attr_name) encrypted_attr_name = "#{attr_name}_encrypted" define_method(encrypted_attr_name) do value = send(attr_name) encrypt(value) end define_method("#{encrypted_attr_name}=") do |value| send("#{attr_name}=", decrypt(value)) end end end private def encrypt(value) value.unpack("H*").first end def decrypt(value) [value].pack("H*") end end

module Encryptable def self.included(mod) mod.extend(ClassMethods) end module ClassMethods def attr_encrypted(attr_name) attr_accessor(attr_name) encrypted_attr_name = "#{attr_name}_encrypted" define_method(encrypted_attr_name) do value = send(attr_name) encrypt(value) end define_method("#{encrypted_attr_name}=") do |value| send("#{attr_name}=", decrypt(value)) end end end private def encrypt(value) value.unpack("H*").first end def decrypt(value) [value].pack("H*") end end card = CreditCard.new card.number = "1234 5678 9012 3456" p card.number # = > "1234 5678 9012 3456" p card.number_encrypted # = > "31323334203536373820393031322033343536" card.number_encrypted = "33343536" p card.number # = > "3456"

So, it's all sunshine and roses?

Static Analysis

Code Readability

# message.rb require "smart_properties" class Message include SmartProperties property! :subject, accepts: String, default: "(No Subject)" property :body, accepts: String property :time, accepts: Time, default: - > { Time.now } end message = Message.new(subject: "New Message", body: "Lorem ipsum dolor sit amet") puts "Message '#{message.subject}' created at #{message.time} has body: #{message.body?}"

# message.rb require "smart_properties" class Message include SmartProperties property! :subject, accepts: String, default: "(No Subject)" property :body, accepts: String property :time, accepts: Time, default: - > { Time.now } end message = Message.new(subject: "New Message", body: "Lorem ipsum dolor sit amet") puts "Message '#{message.subject}' created at #{message.time} has body: #{message.body?}" $ ruby message.rb message.rb:15:in `': undefined method `body?' for # (NoMethodError) Did you mean? body body=

RBI / RBS

# message.rbi # typed: true class Message def subject; end def subject=(value); end def body; end def body=(value); end def time; end def time=(value); end end

$ bundle exec srb tc message.rb:15: Method body? does not exist on Message https://srb.help/7003 15 |puts "Message '#{message.subject}' created at #{message.time} has body: #{message.body?}" ^^^^^^^^^^^^^ # message.rbi # typed: true class Message def subject; end def subject=(value); end def body; end def body=(value); end def time; end def time=(value); end end

Do I have to write RBI fi les?

Tapioca

class Tapioca : : Compilers :: Dsl :: Base extend T :: Sig extend T :: Helpers abstract! sig { abstract.params(tree: RBI : : Tree, constant: T.untyped).void } def decorate(tree, constant); end sig { abstract.returns(T :: Enumerable[Module]) } def gather_constants; end # ... end

class SmartPropertiesGenerator < Tapioca :: Compilers : : Dsl : : Base def decorate(root, smart_prop) properties = smart_prop.properties return if properties.keys.empty? root.create_path(smart_prop) do |klass| properties.values.each do |property| name = property.name.to_s klass.create_method(name) klass.create_method("#{name}=", parameters: [create_param("value", type: "T.untyped")]) end end end def gather_constants ObjectSpace.each_object(Class).select { |c| c < :: SmartProperties } end end

# message.rbi # typed: true class Message sig { returns("T.untyped") } def subject; end sig { params(value: "T.untyped").returns("T.untyped") } def subject=(value); end sig { returns("T.untyped") } def body; end sig { params(value: "T.untyped").returns("T.untyped") } def body=(value); end sig { returns("T.untyped") } def time; end sig { params(value: "T.untyped").returns("T.untyped") } def time=(value); end end

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RBS Rails

Why should I care?

Static Analysis Code Understanding 㱺

$ bin/tapioca dsl User Loading Rails application... Done Loading DSL generator classes... Done Compiling DSL RBI files... Wrote: sorbet/rbi/dsl/user.rbi Done All operations performed in working directory. Please review changes and commit them.

# DO NOT EDIT MANUALLY # This is an autogenerated file for dynamic methods in `User`. # Please instead update this file by running `bin/tapioca dsl User`. # typed: true class User include GeneratedAttributeMethods module GeneratedAttributeMethods sig { returns(T.nilable( : : ActiveSupport :: TimeWithZone)) } def created_at; end sig { params(value: :: ActiveSupport :: TimeWithZone).returns( :: ActiveSupport :: TimeWithZone) } def created_at=(value); end # ... sig { returns(T.nilable( : : String)) } def name; end sig { params(value: T.nilable( :: String)).returns(T.nilable( :: String)) } def name=(value); end # ... sig { returns(T.nilable( : : String)) } def role; end sig { params(value: T.nilable( :: String)).returns(T.nilable( :: String)) } def role=(value); end # ... end

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No content

That's neat, actually!

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