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Enhancing the type system with Refined Types

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.

Juliano Alves

February 14, 2020

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  1. 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
  2. Does it solve the problem? • Java-ish solution • Options

    everywhere • Boilerplate validation code
  3. 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
  4. 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
  5. Why Refined? The compiler does the job Typesafety Uniform (with

    Either) Validation Improves maintainability Expressiveness More precise definition, less tests Easier testing