Enhancing the type system with Refined Types

Sometimes, Ints, Strings and Doubles are not enough: Int has to be greater than 0, String cannot be empty, and Double has to belong inside an interval. What if we could define these restrictions in compile-time? In this talk you will learn about Refined Types, seeing how we can enhance our type system, through the lens of ‘Refined’. Refined is a Scala library for refining types with type-level predicates which constrain the set of values described by the refined type.

Transcript

1. Enhancing the type system
   with Refined Types.
   Juliano Alves
   @vonjuliano
   juliano-alves.com
   

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2. Who am I?
   ● Software Engineer,
   Searcher of perfect modularization,
   Lover of Functional Languages
   ● The cool ones
   Scala, Clojure, Elixir
   ● The "vintage" ones
   Java, C#, Python, Ruby
   @vonjuliano
   juliano-alves.com
   

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3. https://getquill.io
   

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6. Once upon a time...
   

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11. https://blog.codinghorror.com/new-programming-jargon/
    

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15. Tiny Types.
    

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18. (Actually, from ML-family languages)
    

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20. Expressiveness,
    which is strongly
    related to code
    maintainability.
    

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23. Does it solve the problem?
    ● Java-ish solution
    ● Options everywhere
    ● Boilerplate validation code
    

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24. Refinement types.
    

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25. A refinement type is a type
    endowed with a predicate which
    is assumed to hold for any
    element of the refined type.
    …
    Refinement types are thus
    related to behavioral subtyping.
    https://en.wikipedia.org/wiki/Refinement_type
    

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27. refinement type =
    base type + predicate
    

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28. https://github.com/fthomas/refined
    

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30. base type
    +
    predicate
    

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34. Macros explained: THE DARK PLAYGROUND
    

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37. Domain reduction.
    

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38. It makes the compiler work for us.
    

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39. Easier testing, many tests become
    irrelevant.
    

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40. Provided Predicates.
    

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41. Provided Predicates
    ● Boolean (True, False, And, Or)
    ● Char (Letter, Uppercase, Whitespace)
    ● Collection (Contains, Forall, MinSize)
    ● Numeric (Less, Greater, Positive, Interval)
    ● String (Regex, Url, Uuid)
    ● And many more:
    https://github.com/fthomas/refined
    

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42. Using Predicates.
    

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43. Combining predicates: Github Handle
    

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45. How is that useful in the real world?
    

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46. RefinedTypeOps
    

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47. Drawbacks.
    

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48. Compile time.
    

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49. Validation error messages could be
    better.
    

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50. Summary
    

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51. Why Refined?
    The compiler does the job
    Typesafety
    Uniform (with Either)
    Validation
    Improves maintainability
    Expressiveness
    More precise definition, less tests
    Easier testing
    

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52. Thank you!
    @vonjuliano
    juliano-alves.com/
    

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