Ruby3 is a typed language

Ruby3 summit online (https://rhc.connpass.com/event/169873/)

Transcript

1. Ruby3 is a Typed Language
   Soutaro Matsumoto
   

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2. Soutaro Matsumoto
   • Leads the design and implementation of RBS.
   
   • Develops a static type checker for Ruby “Steep”.
   
   • Software Engineer at Square.
   

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3. What is a Typed Language
   • You can write types.
   
   • Type checker find problems.
   class Student {
   fullName: string;
   constructor(public firstName: string, public lastName: str
   this.fullName = firstName + " " + lastName;
   }
   }
   interface Person {
   firstName: string;
   lastName: string;
   }
   function greeter(person: Person): string {
   return "Hello, " + person.first_name + " " + person.lastNa
   }
   let user = new Student("Jane", "User");
   document.body.textContent = greeter(user);
   

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4. What is a Typed Language
   • You can write types.
   
   • Type checker find problems.
   class Student {
   fullName: string;
   constructor(public firstName: string, public lastName: str
   this.fullName = firstName + " " + lastName;
   }
   }
   interface Person {
   firstName: string;
   lastName: string;
   }
   function greeter(person: Person): string {
   return "Hello, " + person.first_name + " " + person.lastNa
   }
   let user = new Student("Jane", "User");
   document.body.textContent = greeter(user);
   

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5. Ruby 2.x
   class Student
   attr_reader :first_name
   attr_reader :last_name
   def initialize(first_name, last_name)
   @first_name = first_name
   @last_name = last_name
   end
   def full_name
   "#{first_name} #{last_name}"
   end
   end
   def greeter(peron)
   "Hello, #{person.first_name} #{person.last_name}"
   end
   user = Student.new("Jane", "User")
   puts greeter(user)
   

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6. Ruby3
   class Student
   attr_reader :first_name
   attr_reader :last_name
   def initialize(first_name, last_name) = @first_name, @last_name = first_name, last_name
   def full_name = "#{first_name} #{last_name}"
   end
   module Greeter
   def self.greet(peron) = "Hello, #{person.first_name} #{person.last_name}"
   end
   user = Student.new("Jane", "User")
   puts Greeter.greet(user)
   

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7. Ruby3
   class Student
   attr_reader :first_name
   attr_reader :last_name
   def initialize(first_name, last_name) =
   @first_name, @last_name = first_name, last_name
   def full_name =
   "#{first_name} #{last_name}"
   end
   module Greeter
   def greet(peron) =
   "Hello, #{person.first_name} #{person.last_name}"
   end
   user = Student.new("Jane", "User")
   puts Greeter.greet(user)
   class Student
   attr_reader first_name: String
   attr_reader last_name: String
   def initialize(String, String) -> void
   def full_name: () -> String
   end
   interface _Person
   def first_name: () -> String
   def last_name: () -> String
   end
   module Greeter
   def self.greet: (_Person) -> String
   end
   

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8. RBS
   • Type declaration for Ruby programs.
   
   • No type annotation in Ruby code, but in
   different files.
   
   • Declare classes, modules, methods, ...
   class Student
   attr_reader first_name: String
   attr_reader last_name: String
   def initialize(String, String) -> void
   def full_name: () -> String
   end
   interface _Person
   def first_name: () -> String
   def last_name: () -> String
   end
   module Greeter
   def greet: (_Person) -> String
   end
   

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9. Ruby3
   • Ruby2 program == Ruby code

   Ruby3 program == Ruby code + RBS.
   
   • Ruby3 will ship with RBS (+ stdlib signatures).
   
   • RBS (+ stdlib signatures) will release as a gem for 2.7 soon.
   
   • Type checkers won't be a part of Ruby.
   

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10. State of RBS
    • https://github.com/ruby/ruby-signature
    
    • No release yet.
    
    • Will rename to RBS ($ gem install rbs).
    
    • PR is open on ruby/ruby for migration.
    
    • PRs from Rubyists!
    
    • Improvements on .rbs files
    
    • Improvements on test features
    

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11. RBS Ecosystem
    • Type checkers
    
    • Steep natively supports RBS.
    
    • type-profiler uses RBS (@mame)
    
    • Integration with existing tools/frameworks
    
    • Translation from/to Sorbet RBI (shopify/rbs_parser)
    
    • Rails support (pocke/rbs_rails)
    

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12. Conclusion
    • Start type checking your Ruby code today!
    

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13. Conclusion
    • Start type checking your Ruby code today!
    
    

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14. 
    Do we need to ship gems with RBS?
    Type checking from IDE?
    I don't want to type check my code.
    RBS is not DRY!
    My code is small.
    Cannot justify the extra cost for type checking.
    I don't want to write types.
    What if a gem doesn't provide RBS?
    How can I write RBS for this?
    
    How about duck typing?
    

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15. RBS Expressiveness
    Union types Interface types
    Method overloading
    class Array[E]
    def []: (Integer) -> E
    | (Integer, Integer) -> Array[E]
    end
    Keyword args
    class Kernel
    private
    def gets: () -> (String | nil) # String?
    end
    interface _ToStr
    def to_str: () -> String
    end
    class String
    def +: (_ToStr) -> String
    end
    class Kernel
    private
    def clone: (?freeze: bool) -> self
    end
    

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16. RBS Expressiveness
    • Supports
    
    • Duck typing (by interface types)
    
    • Open class
    
    • Union types
    
    • Method overloading
    
    • Doesn't support
    
    • Array#map!
    • Meta programming
    
    • Conditional mixin
    a = [1,2,3]
    a.map! { @1.to_s }
    class GPU
    include Win32 if os.windows?
    include Metal if os.mac?
    end
    attr_reader :user
    belongs_to :group
    attr_gzip :content
    

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17. Type Checking Options
    1. Type checking using a static type checker.
    
    2. No type checking.
    
    3. Between 1 and 2.
    Chose the best option for your project.
    

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18. Using Static Type Checker
    • Pros
    
    • Fully utilize type checker
    
    • LSP based integrations provide better
    coding experience.
    
    • Cons
    
    • You have to take care of RBS
    
    • You have to write type-checking
    compatible code
    

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19. Using Static Type Checker
    • Pros
    
    • Fully utilize type checker
    
    • LSP based integrations provide better
    coding experience.
    
    • Cons
    
    • You have to take care of RBS
    
    • You have to write type-checking
    compatible code
    

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20. “My Code is Small”
    • 100 lines of Ruby code is worth type checking.
    
    • Small programs sometimes use generic data structures like Array/Hash.
    Let type checkers manage the data structure.
    

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21. Coding with Type Checker
    class Student
    end
    

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22. Coding with Type Checker
    class Student
    end
    sig/student.rbs
    

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23. class Student
    attr_reader first_name: String
    attr_reader last_name: String
    def initialize(String, String) -> void
    def full_name: () -> String
    end
    sig/student.rbs
    

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24. class Student
    attr_reader first_name: String
    attr_reader last_name: String
    def initialize(String, String) -> void
    def full_name: () -> String
    end
    sig/student.rbs
    lib/student.rb
    class Student
    attr_reader :first_name
    attr_reader :last_name
    def initialize(first_name, last_name) =
    @first_name, @last_name = first_name, last_name
    def full_name =
    "#{first_name} #{last_name}"
    end
    

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25. class Student
    attr_reader first_name: String
    attr_reader last_name: String
    def initialize(String, String) -> void
    def full_name: () -> String
    end
    sig/student.rbs
    interface _Person
    def first_name: () -> String
    def last_name: () -> String
    end
    module Greeter
    def self.greet: (_Person) -> String
    end
    sig/greeter.rbs
    

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26. class Student
    attr_reader first_name: String
    attr_reader last_name: String
    def initialize(String, String) -> void
    def full_name: () -> String
    end
    sig/student.rbs
    interface _Person
    def first_name: () -> String
    def last_name: () -> String
    end
    module Greeter
    def self.greet: (_Person) -> String
    end
    sig/greeter.rbs
    lib/main.rb
    user = Student.new("Jane", "User")
    puts Greeter.greet(user)
    

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27. class Student
    attr_reader first_name: String
    attr_reader last_name: String
    def initialize(String, String) -> void
    def full_name: () -> String
    end
    sig/student.rbs
    interface _Person
    def first_name: () -> String
    def middle_name: () -> String?
    def last_name: () -> String
    end
    module Greeter
    def self.greet: (_Person) -> String
    end
    sig/greeter.rbs
    lib/main.rb
    user = Student.new("Jane", "User")
    puts Greeter.greet(user)
    

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28. class Student
    attr_reader first_name: String
    attr_reader last_name: String
    def initialize(String, String) -> void
    def full_name: () -> String
    end
    sig/student.rbs
    interface _Person
    def first_name: () -> String
    def middle_name: () -> String?
    def last_name: () -> String
    end
    module Greeter
    def self.greet: (_Person) -> String
    end
    sig/greeter.rbs
    lib/main.rb
    user = Student.new("Jane", "User")
    puts Greeter.greet(user)
    

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29. Coding with Type Checker
    • Design API before implementation.
    Design Doc Test Implementation
    Abstract Concrete
    Works (Revenue)
    Executable (pass/fail)
    Human readable (review)
    

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30. Coding with Type Checker
    • Design API before implementation.
    Design Doc Test Implementation
    Abstract Concrete
    Works (Revenue)
    Executable (pass/fail)
    Human readable (review)
    Type check
    Verifiable
    

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31. Type Check Partially
    • What if app already exists?
    
    • Type checkers allows mixing typed and untyped Ruby code.
    
    • App code vs test code.
    
    • Models vs controller.
    
    • This file cannot be typed.
    lib/student.rb
    eval <<-SRC
    class Student
    def method_missing(name, *args)
    case name
    when :first_name
    @first_name
    sig/student.rbs
    class Student
    attr_reader first_name: String
    attr_reader last_name: String
    def initialize: (String, String) -> void
    end
    

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32. lib/person.rb
    class Student
    attr_reader :first_name
    attr_reader :last_name
    def initialize(first_name, last_name) =
    @first_name, @last_name = first_name, last_name
    def full_name =
    "#{first_name} #{last_name}"
    end
    lib/greeter.rb
    module Greeter
    def self.greeter(person) =
    "Hello, #{person.first_name} #{person.last_name}"
    end
    require "person"
    require "greeter"
    user = Student.new("Jane", "User")
    puts greeter(user)
    lib/main.rb
    

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33. lib/person.rb
    class Student
    attr_reader :first_name
    attr_reader :last_name
    def initialize(first_name, last_name) =
    @first_name, @last_name = first_name, last_name
    def full_name =
    "#{first_name} #{last_name}"
    end
    lib/greeter.rb
    module Greeter
    def self.greeter(person) =
    "Hello, #{person.first_name} #{person.last_name}"
    end
    require "person"
    require "greeter"
    user = Student.new("Jane", "User")
    puts greeter(user)
    lib/main.rb
    sig/person.rbs
    class Student
    attr_reader first_name: String
    attr_reader last_name: String
    def initialize: (String, String) -> void
    def full_name: () -> String
    end
    

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34. lib/person.rb
    class Student
    attr_reader :first_name
    attr_reader :last_name
    def initialize(first_name, last_name) =
    @first_name, @last_name = first_name, last_name
    def full_name =
    "#{first_name} #{last_name}"
    end
    lib/greeter.rb
    module Greeter
    def self.greeter(person) =
    "Hello, #{person.first_name} #{person.last_name}"
    end
    require "person"
    require "greeter"
    user = Student.new("Jane", "User")
    puts greeter(user)
    lib/main.rb
    sig/person.rbs
    class Student
    attr_reader first_name: String
    attr_reader last_name: String
    def initialize: (String, String) -> void
    def full_name: () -> String
    end
    sig/greeter.rbs
    interface _Person
    def first_name: () -> String
    def last_name: () -> String
    end
    module Greeter
    def self.greet: (_Person) -> Strin
    end
    

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35. Type Checking Options
    1. No type checking.
    
    2. Type checking using a static type checker.
    
    3. Between 1 and 2.
    

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36. RBS without Type Checker
    • You write RBS but don't use type checker.
    
    • Pros
    
    • You can help your gem users type check their programs.
    
    • You don't have to write type-checker compatible code.
    
    • Cons
    
    • You cannot type check.
    

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37. Writing RBS
    • You don't have to write perfect RBS.
    
    • List of methods/classes of untyped is okay.
    
    • Write methods you really need to type check your code.
    class CSV
    def self.read: (String) -> Array[Array[String]]
    end
    sig/polyfill/csv.rbs
    class IO
    def self.popen: (*untyped args) -> untyped
    end
    sig/polyfill/io.rbs
    

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38. rbs prototype
    $ bundle exec rbs prototype runtime Integer
    class Integer < Numeric
    include JSON::Ext::Generator::GeneratorMethods::Integer
    def self.sqrt: (untyped) -> untyped
    public
    def %: (untyped) -> untyped
    def &: (untyped) -> untyped
    def *: (untyped) -> untyped
    Prints list of classes, modules, includes and methods.
    
    Replace untypeds with precise types.
    

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39. Runtime Type Check
    • Opt-in runtime type check with RBS definition.
    
    • Technically possible, does anyone want this?
    $ RUBYOPT="-rbundler/setup -rrbs/test/runtime" \
    RBS_RUNTIME_CHECK_TARGETS='Optcarrot::*' \
    bundle exec rake test
    

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40. Inline Type Annotations
    • A feature of type checkers.
    
    • [Steep] Not yet, but worth considering.
    class Student
    attr_reader :first_name # @type String
    attr_reader :last_name # @type String
    # @type (String, String) -> void
    def initialize(first_name, last_name) =
    @first_name, @last_name = first_name, last_name
    # @type () -> String
    def full_name = "#{first_name} #{last_name}"
    end
    

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41. Inline Type Annotations
    • A feature of type checkers.
    
    • No plan yet, but worth considering.
    class Student < ApplicationRecord
    include Enumerable # including Enumerable[Student]
    # @type method classes: () -> ActiveRecord::Relation[Student]
    # @type method class_ids: () -> ActiveRecord::IDRelation
    has_many :classes
    # @type (University, classes: Array[ClassDefinition], requirements: Requirement, credits: Integer) -> Ar
    def minimum_classes_to_graduations(univ, classes:, requirements:, credits:)
    ...
    end
    end
    

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42. 
    Do we need to ship gems with RBS?
    Type checking from IDE?
    I don't want to type check my code.
    RBS is not DRY!
    My code is small.
    Cannot justify the extra cost for type checking.
    I don't want to write types.
    What if a gem doesn't provide RBS?
    How can I write RBS for this?
    
    How about duck typing?
    

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43. I don't want to write types.
    

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