Scala 不成形镜片奇怪的行为

我试图将我的case类转换为一个序列，每个字段包含一个镜头。我创建了以下简化示例来突出我遇到的问题

以下代码将给出运行时错误：

import shapeless._

case class Testing(field1: String, field2: Double)

val lenses = Seq(0,1).map(i => lens[Testing] >> i)

鉴于以下情况不适用：

import shapeless._

case class Testing(field1: String, field2: Double)

val lens1 = lens[Testing] >> 0
val lens2 = lens[Testing] >> 1

val lenses = Seq(lens1, lens2)

实际错误为“表达式i的计算结果不是非负整数文字”

我觉得这个错误消息是误导性的，因为代码val lens3=lens[Testing]>>2（即访问一个字段太多）会给出相同的错误消息

有没有人在《变形》中经历过这样的行为？在我的Case类中，有没有一种更简单的方法可以将每个字段的元素镜头提取到一个序列中（例如，不像monocle中的@lens，您仍然需要使用字段名访问每个镜头）

隐式转换为

lens[Testing] >> Nat._0
lens[Testing] >> Nat._1

这是有效的，但是

val lenses = Seq(0,1).map(i => lens[Testing] >> i)

或者

val lens=Seq（Nat.\u 0，Nat.\u 1）。map（i=>lens[Testing]>>i）

没有

Seq（Nat.\u 0，Nat.\u 1）

具有类型

Seq[Nat]

，因此

i

具有类型

Nat

（而不是特定的

Nat.\u 0

，

Nat.\u 1

），这太粗糙了

以下构造透镜的

HList

（而不是

Seq

）的方法似乎有效：

  import shapeless.{::, Generic, HList, HNil, Lens, MkHListSelectLens}

  case class Testing(field1: String, field2: Double)

  trait MkLensHlist[A] {
    type Out <: HList
    def apply(): Out
  }

  object MkLensHlist {
    type Aux[A, Out0 <: HList] = MkLensHlist[A] { type Out = Out0 }
    def instance[L, Out0 <: HList](x: Out0): Aux[L, Out0] = new MkLensHlist[L] {
      override type Out = Out0
      override def apply(): Out0 = x
    }

    def apply[A](implicit instance: MkLensHlist[A]): instance.Out = instance()

    implicit def mk[A, L <: HList, Out <: HList](implicit
                                                 gen: Generic.Aux[A, L],
                                                 apply: ApplyMkHListSelectLens.Aux[L, Out]
                                                ): Aux[A, Out] = instance(apply())
  }

  trait ApplyMkHListSelectLens[L <: HList] {
    type Out <: HList
    def apply(): Out
  }

  object ApplyMkHListSelectLens {
    type Aux[L <: HList, Out0 <: HList] = ApplyMkHListSelectLens[L] { type Out = Out0}
    def instance[L <: HList, Out0 <: HList](x: Out0): Aux[L, Out0] = new ApplyMkHListSelectLens[L] {
      override type Out = Out0
      override def apply(): Out0 = x
    }

    implicit def mk[L <: HList, Out <: HList](implicit
                                              apply: ApplyMkHListSelectLens1.Aux[L, L, Out]
                                             ): Aux[L, Out] =
      instance(apply())
  }


  trait ApplyMkHListSelectLens1[L <: HList, L1 <: HList] {
    type Out <: HList
    def apply(): Out
  }

  object ApplyMkHListSelectLens1 {
    type Aux[L <: HList, L1 <: HList, Out0 <: HList] = ApplyMkHListSelectLens1[L, L1] { type Out = Out0}
    def instance[L <: HList, L1 <: HList, Out0 <: HList](x: Out0): Aux[L, L1, Out0] = new ApplyMkHListSelectLens1[L, L1] {
      override type Out = Out0
      override def apply(): Out0 = x
    }

    implicit def mk1[L <: HList, H, T <: HList, Out <: HList](implicit
                                                             lens: MkHListSelectLens[L, H],
                                                             apply: Aux[L, T, Out]
                                                            ): Aux[L, H :: T, Lens[L, H] :: Out] =
      instance(lens() :: apply())

    implicit def mk2[L <: HList]: Aux[L, HNil, HNil] =
      instance(HNil)
  }

  MkLensHlist[Testing] 
  // shapeless.MkHListSelectLens$$anon$36$$anon$17@340f438e :: shapeless.MkHListSelectLens$$anon$36$$anon$17@30c7da1e :: HNil

import shapeless.{：：，Generic，HList，HNil，Lens，MkHListSelectLens}
案例类测试（字段1:字符串，字段2:双精度）
特征列表[A]{
打字
  import shapeless.{::, Generic, HList, HNil, Lens, MkHListSelectLens}

  case class Testing(field1: String, field2: Double)

  trait MkLensHlist[A] {
    type Out <: HList
    def apply(): Out
  }

  object MkLensHlist {
    type Aux[A, Out0 <: HList] = MkLensHlist[A] { type Out = Out0 }
    def instance[L, Out0 <: HList](x: Out0): Aux[L, Out0] = new MkLensHlist[L] {
      override type Out = Out0
      override def apply(): Out0 = x
    }

    def apply[A](implicit instance: MkLensHlist[A]): instance.Out = instance()

    implicit def mk[A, L <: HList, Out <: HList](implicit
                                                 gen: Generic.Aux[A, L],
                                                 apply: ApplyMkHListSelectLens.Aux[L, Out]
                                                ): Aux[A, Out] = instance(apply())
  }

  trait ApplyMkHListSelectLens[L <: HList] {
    type Out <: HList
    def apply(): Out
  }

  object ApplyMkHListSelectLens {
    type Aux[L <: HList, Out0 <: HList] = ApplyMkHListSelectLens[L] { type Out = Out0}
    def instance[L <: HList, Out0 <: HList](x: Out0): Aux[L, Out0] = new ApplyMkHListSelectLens[L] {
      override type Out = Out0
      override def apply(): Out0 = x
    }

    implicit def mk[L <: HList, Out <: HList](implicit
                                              apply: ApplyMkHListSelectLens1.Aux[L, L, Out]
                                             ): Aux[L, Out] =
      instance(apply())
  }


  trait ApplyMkHListSelectLens1[L <: HList, L1 <: HList] {
    type Out <: HList
    def apply(): Out
  }

  object ApplyMkHListSelectLens1 {
    type Aux[L <: HList, L1 <: HList, Out0 <: HList] = ApplyMkHListSelectLens1[L, L1] { type Out = Out0}
    def instance[L <: HList, L1 <: HList, Out0 <: HList](x: Out0): Aux[L, L1, Out0] = new ApplyMkHListSelectLens1[L, L1] {
      override type Out = Out0
      override def apply(): Out0 = x
    }

    implicit def mk1[L <: HList, H, T <: HList, Out <: HList](implicit
                                                             lens: MkHListSelectLens[L, H],
                                                             apply: Aux[L, T, Out]
                                                            ): Aux[L, H :: T, Lens[L, H] :: Out] =
      instance(lens() :: apply())

    implicit def mk2[L <: HList]: Aux[L, HNil, HNil] =
      instance(HNil)
  }

  MkLensHlist[Testing] 
  // shapeless.MkHListSelectLens$$anon$36$$anon$17@340f438e :: shapeless.MkHListSelectLens$$anon$36$$anon$17@30c7da1e :: HNil