Newtype coersion with newtype > 0.4.4

in newtype 0.4.4 repr becomes a private

https/repo1.maven.org/maven2/io/estatico/newtype_2.13/0.4.4/newtype_2.13-0.4.4-sources.jar!/io/estatico/newtype/Coercible.scala

final class CoercibleIdOps[A](private val repr: A) extends AnyVal {
  @inline def coerce[B](implicit ev: Coercible[A, B]): B = repr.asInstanceOf[B]
}

thus

  implicit def coercibleEncoder[A: Coercible[B, *], B: Encoder]: Encoder[A] =
    Encoder[B].contramap(_.repr.asInstanceOf[B])

pfps-shopping-cart/modules/core/src/main/scala/shop/http/json.scala:46:28: value repr is not a member of type parameter A
[error]     Encoder[B].contramap(_.repr.asInstanceOf[B])

[gvolpe]

The approach using scalaz-deriving is quite reasonable (more a la Haskell) but unfortunately doesn’t support derivation for typeclasses from projects such as http4s and ciris.

Still, we can take advantage of Scala not being Haskell and do it generally whenever we can, even at the expense of using a safe casting technique.

[stale[bot]]

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