CODEWITHSUNDEEP
scalatypeclassshapeless
outlaw
outlaw

Reputation: 241

Scala refined types and type class derivation (Shapeless)

I am learning about shapeless type class derivation. One common exercises is to generate a random instance of a given case class. Simply put, the idea is to have something like the following:

trait Random[C] {
  def gen: C
}

// primitives' instances
implicit val rs: Random[String] = ...
implicit val rd: Random[Boolean] = ...
implicit val rb: Random[Boolean] = ...

// HList and HNil instances
implicit val rhlist: Random[H :: T] = ...
implicit val rhnil: Random[HNil]

With an implicit shapeless.Generic[C], we can have then a random instance of C. This works well, however I want my generator to respect some rules. For example, Random[Double] should also generate not only a random double, but one that respects some bounds. The bound can be provided using an annotation on that field (case class Foo(@GreaterThan(0) x: Double)) or using refined types (case class Foo(x: Double Refined Positive)).

I am aware that the refined types approach might be totally different than annotations. I would like to explore both approaches, or the more idiomatic one. Do you have any hints ? Thanks

Upvotes: 0

Views: 113

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