Ruby Programming with Type Checking

RubyKaigi 2018

Transcript

1. Ruby Programming with Type Checking Soutaro Matsumoto (@soutaro)
2. Steep • https://github.com/soutaro/steep • Gradual typing for Ruby • Type annotation as a comment • Type definitions by programmers • Local type inference • Structural subtyping (between object types)
3. Released 0.3.0, yesterday
4. Released 0.3.0, yesterday Automatic implements Type-case on case expression Branch specific type annotation Constant type declaration Instance variable type declaration Typing polymorphic methods Revised type inference algorithm nil type Casting to any type masgn support Scaffolding type definitions
5. Comparison with Sorbet Steep Sorbet Type Inference Local Type Inference Type System Generics, union type, any type, context sensitive typing Subtyping Structural Nominal Signature Special Syntax in Another File Ruby code Type Annotation Comment Ruby code Performance Slow Fast
6. Demo • Introductory example • Simple Ruby program with two classes
7. Type Checking Steps 1. Write signatures 2. Write Ruby program with annotation 3. Run type checker 4. Goto 1 (2)
8. Demo • Type checking existing Ruby program • 4 years old production Rails application
9. Strategy • Even though Rails uses a lot of metaprogramming, there is a concrete type representation eventually • Programmers can write down that application's state as type definitions
10. • 1 controller / 2 models • Minimal set of classes/methods Demo Result
11. • 1 controller / 2 models • Minimal set of classes/methods Demo Result
12. • 1 controller / 2 models • Minimal set of classes/methods Demo Result For Models
13. • 1 controller / 2 models • Minimal set of classes/methods Demo Result For Rails
14. • 1 controller / 2 models • Minimal set of classes/methods Demo Result For Other Libraries
15. Only 7 lines of annotations
16. Type Checking Difficulties • Missing library types • Type system expressiveness (params) • Abused metaprogramming (ActiveRecord)
17. Missing Library Types • 40% of the signatures I wrote was type of libraries • If you ship your gems with type definitions, we can use that without writing their signatures
18. Type System Expressiveness • Tuple types and record types can improve • Workaround: Use ActionArgs ⚡
 def show: (id: Integer, org_id: Integer) -> void def params: -> Hash<Symbol | String, any> def params: -> { id: String, org_id: String } Not Implemented Yet
19. Abused Metaprogramming • Steep itself does not understand Rails association methods (has_many) or even builtin ones (attr_reader) • Generate signatures by some tools with Rails knowledge • A plugin to generate signature from AR models? • Smarter scaffold command?
20. Recap • Try Ruby programming with type checking using Steep
 $ gem install steep • Give me a feedbacks!