在 Scala 3 中打印 MirroredElemTypes

Question

I am trying to modify this standard example to print values with the types. And I am stuck with p.MirroredElemTypes . I haven't found any API to traverse and stringify types.

Answer 1

To check MirroredElemTypes you can just summon

import scala.deriving.Mirror

case class A(i: Int, s: String, b: Boolean)

val m = summon[Mirror.Of[A]]
summon[m.MirroredElemTypes =:= (Int, String, Boolean)] // compiles

But if you want to print MirroredElemTypes you can do the following.

For some reason Typeable doesn't work now but in its error message it prints the type

// scalaVersion := "3.0.2"
// libraryDependencies += "org.typelevel" %% "shapeless3-typeable" % "3.0.3"
import shapeless3.typeable.Typeable

summon[Typeable[m.MirroredElemTypes]].describe
// Typeable for sum type scala.*:[scala.Int, scala.*:[scala.Predef.String, scala.*:[scala.Boolean, scala.Tuple$package.EmptyTuple]]] with no Mirror

Alternatively you can write a simple macro

import scala.quoted.*

inline def describe[A]: String = ${describeImpl[A]}

def describeImpl[T: Type](using Quotes): Expr[String] = {
  import quotes.reflect.*
  Literal(StringConstant(TypeRepr.of[T].dealias.show)).asExprOf[String]
}

// in a different file
describe[m.MirroredElemTypes]
// scala.*:[scala.Int, scala.*:[scala.Predef.String, scala.*:[scala.Boolean, scala.Tuple$package.EmptyTuple]]]