[Q] [1.7.x] Patching -- How can I use a Option[F[T]] as Option[Option[T]]?

[stivens]

The code below works in version 1.6, but it does not work in version 1.7. How can this be fixed?

import io.scalaland.chimney.dsl._
import io.scalaland.chimney.Transformer

case class Clearable[T](value: Option[T])
object Clearable {
  def someValueUpdate[T](value: T): Option[Clearable[T]] = Some(Clearable.set(value))
  def someCleanup[T]: Option[Clearable[T]]               = Some(Clearable.clear)
  def set[T](value: T): Clearable[T]                     = Clearable(Some(value))
  def clear[T]: Clearable[T]                             = Clearable(Option.empty[T])
}


case class Person(id: Int, firstname: String, lastname: String, note: Option[String], email: Option[String], address: Option[String])

case class PersonUpdate(
  note: Option[Clearable[String]] = None,
  email: Option[Clearable[String]] = None,
  address: Option[Clearable[String]] = None
)

val p1 = Person(0, "Joe", "Doe", Some("note"), Some("[email protected]"), Some("Example Street 42"))

given clearableTransformer[T]: Transformer[Clearable[T], Option[T]] = (src: Clearable[T]) => src.value

val updated = p1.patchUsing(PersonUpdate(note = Clearable.someValueUpdate("new note"), address = Clearable.someCleanup))

println(updated)

Chimney can't derive patching for Playground.Person with patch type Playground.PersonUpdate

Playground.Person
note: scala.Option[java.lang.String] - can't derive transformation from note: scala.Option[Playground.Clearable[java.lang.String]] in source type Playground.PersonUpdate
email: scala.Option[java.lang.String] - can't derive transformation from email: scala.Option[Playground.Clearable[java.lang.String]] in source type Playground.PersonUpdate
address: scala.Option[java.lang.String] - can't derive transformation from address: scala.Option[Playground.Clearable[java.lang.String]] in source type Playground.PersonUpdate

java.lang.String
derivation from clearable: Playground.Clearable[java.lang.String] to java.lang.String is not supported in Chimney!

Consult https://chimney.readthedocs.io for usage examples.

[MateuszKubuszok]

You can either:

• create an implicit Patcher to update Option[T] with Option[Clearable[T]] - it's quick and easy, but hardcodes all the types
• inform Chimney that Clearable[T] is like an Option[T] - Option[Option[T]] have the semantics that you seem to want here - it a bit more work but it's more flexible

https://scastie.scala-lang.org/MateuszKubuszok/Z01iEi49QTqKjmju3afPcg

[stivens]

thanks!