Ruby Programming with Type Checking

RubyKaigi 2018

Transcript

1. Ruby Programming with
   Type Checking
   Soutaro Matsumoto
   
   (@soutaro)
   

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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)
   

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3. Released 0.3.0, yesterday
   

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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
   

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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
   

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6. Demo
   • Introductory example
   
   • Simple Ruby program with two classes
   

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7. Type Checking Steps
   1. Write signatures
   
   2. Write Ruby program with annotation
   
   3. Run type checker
   
   4. Goto 1 (2)
   

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8. Demo
   • Type checking existing Ruby program
   
   • 4 years old production Rails application
   

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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
   

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10. • 1 controller / 2 models
    
    • Minimal set of classes/methods
    Demo Result
    

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11. • 1 controller / 2 models
    
    • Minimal set of classes/methods
    Demo Result
    

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12. • 1 controller / 2 models
    
    • Minimal set of classes/methods
    Demo Result
    For Models
    

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13. • 1 controller / 2 models
    
    • Minimal set of classes/methods
    Demo Result
    For Rails
    

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14. • 1 controller / 2 models
    
    • Minimal set of classes/methods
    Demo Result
    For Other Libraries
    

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15. Only 7 lines of annotations
    

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16. Type Checking Difficulties
    • Missing library types
    
    • Type system expressiveness (params)
    
    • Abused metaprogramming (ActiveRecord)
    

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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
    

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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
    def params: -> { id: String, org_id: String }
    Not Implemented Yet
    

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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?
    

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20. Recap
    • Try Ruby programming with type checking using Steep

    $ gem install steep
    
    • Give me a feedbacks!
    

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