Selectable and type inference

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1

Related to my previous question, but in a somewhat different direction…

I’m trying to use Selectable to easily introspect classes for their fields and corresponding types. I have the following strawman:

//> using options -experimental -language:experimental.namedTuples

import scala.reflect.ClassTag

case class Field[T](name: String)(using val classTag: ClassTag[T])

class FieldSelector[T: ClassTag as classTag]() extends Selectable:
  type Fields = NamedTuple.Map[NamedTuple.From[T], Field]
  // QUESTION: How can I specify the type parameter of Field[_]
  //           to be the type of the field corresponding to `fieldName`
  def selectDynamic(fieldName: String) = Field(fieldName)

case class Person(name: String, age: Int)

@main def test =
  val field = FieldSelector[Person].age // correctly inferred as Field[Int]
  assert(field.name == "age")
  println(field.classTag.runtimeClass) // prints "class Person" ???
  assert(field.classTag.runtimeClass == classOf[Int]) // assertion failed

However as noted above, I’m not quite getting what I want. I’d love to construct a Field[Int]("age") – which is correctly being inferred at the callsite where I call .age – but it looks like what’s being constructed inside selectDynamic is a Field[Person]("age") instead.

Any ideas how to do this?

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