Expand case class default values example

[evbo]

Hi,

I think this defaultParamsInference is a great example I'd like to extend further to include the type of each case class field.

What amazes me is I didn't realize you can cast a Tree as you do here: https://github.com/lampepfl/dotty-macro-examples/blob/main/defaultParamsInference/src/macro.scala#L18

I thought I would need to use the Symbol's signature to get the type but I don't see a lot of documentation for signature or how to access type information (such as individually selecting types from higher orders, such as List[Int], as enabled in scala 2 by typeSignature or scala.reflect.macros.Context.typeCheck).

So can someone please clarify how tree or signature can be used to get detailed type information for each case class field?

Thanks!

[evbo]

it seems getting type information is indeed not easy, as discussed here: https://github.com/lampepfl/dotty/issues/13553

They've since added https://github.com/lampepfl/dotty/pull/14124 but it is labeled experimental so not yet usable in stable builds.

[evbo]

Got it and there's a few ways to skin this cat, but this one I like the most from Gael since it accounts for higher kinds: https://stackoverflow.com/a/69073868/1080804

example:

// for a cc field of type Map[String, List[Int]], this gives you:
// Map, String, and List TypeReprs
// recursion may be necessary to get List[Int]: https://stackoverflow.com/a/69073868/1080804
val typeParams: List[TypeRepr] = ccField.owner.typeRef.memberType(ccField) match {
  // from: https://docs.scala-lang.org/scala3/guides/contribution/arch-types.html
  case AppliedType(thisType, args) => List(thisType) ++ args
  case _              => Nil
}

val simpleStrings = typeParams.map(_.typeSymbol.fullName)