Ruby programming with types in action

RubyKaigi 2022 -- Tsu, Mie, Japan
September 10, 2022

Transcript

1. Soutaro Matsumoto (@soutaro)
   Ruby programming with types
   in action
   This work by RubyKaigi 2022 Team is licensed under a Creative Commons Attribution 4.0 Unported License.
   #BF4545 #B8A562 #755B8E #4E6994 #41414F #2C2C31 UFYUDPMPS
   
   

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2. @soutaro
   • Developer of Steep & RBS
   
   • Ruby committer
   
   • Working for Square Block
   Soutaro Matsumoto
   

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3. RBS & Steep
   • We have
   fi
   ve talks related to RBS/Steep this year
   
   • Generating RBS is big topic
   
   • How can we use the type de
   fi
   nitions?
   
   • Show people the types instead of callseq
   
   • Type checking! 💪
   

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4. RBS 2.7.0.pre.1
   Updates since Ruby 3.1 (RBS 2.0)
   • Type of self in blocks/procs (Steep 1.2 will support)
   
   • Batch prototype (RBS 2.5)
   
   • $ rbs prototype rb --out-dir=sig/app app
   
   
   • RDoc plugin (Supported by Google Summer of Code)
   
   • $ rdoc sig
   def foo: { () [self: String] -> void } -> void
   def instance_eval: [A] { () [self: self] -> A } -> A
   $ gem install rbs --pre
   

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5. Type checking benefits
   When we have a typed Ruby code base
   • Understanding code
   
   • API documentation
   
   • Adding a new feature
   
   • Refactoring the feature
   

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6. Demo
   What can we do with typed Ruby code
   • Hover
   
   • Goto de
   fi
   nition
   
   • Completion
   
   • Type errors
   

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7. Demo
   

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8. Demo 2
   Getting started with Steep
   1. Setup
   
   2. Generate RBS
   fi
   le prototypes
   
   3. Run type checker
   
   4. Add more types
   

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9. Demo app
   • Point-of-sale app
   
   • Models
   
   • Order
   
   • OrderItem
   
   • CashPayment
   
   • CardPayment
   

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10. Demo app
    • Point-of-sale app
    
    • Models
    
    • Order
    
    • OrderItem
    
    • CashPayment
    
    • CardPayment
    

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11. Demo app
    • Point-of-sale app
    
    • Models
    
    • Order
    
    • OrderItem
    
    • CashPayment
    
    • CardPayment
    

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12. Demo 2
    

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13. Focus on the part you work on
    • You don't have to
    fi
    x all of the type errors when you start
    
    • Give types to the related part as you need
    
    • Type checking a few small
    fi
    les would be good for exercise
    Detected 1759 problems from 85 files
    

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14. Focus on the part you work on
    • You don't have to
    fi
    x all of the type errors when you start
    
    • Give types to the related part as you need
    
    • Type checking a few small
    fi
    les would be good for exercise
    Detected 1759 problems from 85 files
    

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15. Make your code safe against nil
    • The only one way to handle nil safely: test every time before using it
    
    • Optional type helps you
    # @type var order: Order?
    
    
    if order = Order.find_by(id: params[:id])
    
    
    order.update(...)
    
    
    else
    
    
    render status: :not_found
    
    
    end
    # def sample: () -> Element?
    
    
    unless array.empty?
    
    
    random = array.sample or raise
    
    
    end
    Do something else if nil It cannot happen
    

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16. Help Steep type check your code
    # @type var out_dir: Pathname?
    
    
    out_dir = nil
    
    
    # @type var pairs: Array[[String, Integer]]
    
    
    pairs = []
    Declare the variable types
    Cast to untyped or skip type checking 1 + (_ = "")
    
    
    __skip__ = 1 + ""
    MoneyData = Struct.new(:currency, :amount) do
    
    
    # @implements MoneyData
    
    
    def exchange_to(currency, rate)
    Support meta-programming
    

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17. Writing new code
    • Type checking existing code is 😫
    
    • You know there is no critical bug there
    
    • Steep will detect minor problems that forces you add workarounds
    
    • Many e
    ff
    orts, little bene
    fi
    ts
    
    • Let's write new code with Steep 💪
    
    • There must be unknown bugs
    

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18. Demo 3
    Adding new feature with types
    • De
    fi
    ning APIs in RBS
    
    • Writing implementation with type checker
    

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19. Add search feature
    "ca
    ff
    e latte"
    

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20. Add search feature
    "ca
    ff
    e latte" before:2022-08-01 paid-by:cash
    

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21. Demo 3
    

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22. Inheritance vs union types
    • Choose one that is more suitable for the problem
    
    • Steep helps you keep case-when safe and up to date
    # @type var query: Query::Base
    
    
    query.build_relation()
    # @type var query: Query::Name | Query::Before | Quer
    
    
    case query
    
    
    when Query::Name
    
    
    ...
    
    
    when Query::Before
    
    
    ...
    
    
    when Query::PaidBy
    
    
    ...
    
    
    end
    Inheritance Union types
    

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23. Inheritance vs union types
    • Inheritance 㱻 method call, union types 㱻 case-when
    
    • Known set of data types → union types + case-when

    Unknown set of data types → inheritance + method call
    
    • Expression problem
    
    • Union types are generalization of optional types
    
    • Integer? == Integer | nil
    
    • Union types help you enumerate all cases
    

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24. Working with types
    • Types are abstraction of your code
    
    • Easier to write/change than implementation/tests
    
    • Validates consistencies between components unlike design docs
    
    • Type de
    fi
    nitions and implementation are iterative
    
    • Write types → write code → types → code → ...
    App code Tests RBS
    Design docs
    
    Whiteboard
    Detailed Abstract
    

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25. Working with types
    • Types are abstraction of your code
    
    • Easier to write/change than implementation/tests
    
    • Validates consistencies between components unlike design docs
    
    • Type de
    fi
    nitions and implementation are iterative
    
    • Write types → write code → types → code → ...
    App code Tests RBS
    Design docs
    
    Whiteboard
    Detailed Abstract
    

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26. Can I do it with RubyMine?
    • RubyMine has limited support for Steep
    
    • But, it provides another type checker integrated with RBS, and you can
    develop Ruby programs with types using RubyMine
    

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27. Recap
    • More bene
    fi
    t from types when you write new code
    
    • Writing types and implementation
    
    • Anti-patterns without types can be a best practice
    
    • Easier trial and error with types than with implementation
    

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