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scala - 从 Mirror 获取 MirroredElemLabels

问题描述

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

编辑：这是尝试使用时产生编译器错误的代码summonAll

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 @ _]

标签： scalagenericsshapelesstype-level-computationscala-3

解决方案

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

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