从镜像中获取 MirroredElemLabels

问题描述

Scala 3 的 scala.deriving.Mirror 有一个类型成员 MirroredElemLabels，它是一个字符串文字元组。将该类型作为值的标准方法是什么？

编辑：here's the code 尝试使用 summonAll

会产生编译器错误

case class Test(a: Int,b: String)
val mirror = implicitly[Mirror.ProductOf[Test]]
val labels = summonAll[mirror.MirroredElemLabels]
println(labels)

---

cannot reduce inline match with
 scrutinee:  compiletime.erasedValue[App.mirror.MirroredElemLabels] : App.mirror.MirroredElemLabels
 patterns :  case _:EmptyTuple
             case _:*:[t @ _,ts @ _]

解决方法

尝试使用 scala.ValueOf

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

import scala.deriving.Mirror
import scala.compiletime.summonAll

val mirror = summon[Mirror.Of[A]]    
type ValueOfs = Tuple.Map[mirror.MirroredElemLabels,ValueOf]
val valueOfs = summonAll[ValueOfs]

def values(t: Tuple): Tuple = t match
  case (h: ValueOf[_]) *: t1 => h.value *: values(t1)
  case EmptyTuple => EmptyTuple

values(valueOfs) // (i,s)

http://dotty.epfl.ch/docs/reference/contextual/derivation.html