使用 shapeless 获取案例类字段的名称和类型 [英] Get case class field's name and type with shapeless

问题描述

是否可以通过shapeless获取scala case类字段的名称和类型?

Is it possible to get scala case class field's names and types with shapeless?

我试过这样(T是case类):

I've tried like this (T is case class):

trait Cpo[T] {

def withPrimaryKey[R <: HList, K, V <: HList](f: Seq[Symbol] => Seq[Symbol])(
    implicit labellGeneric: LabelledGeneric.Aux[T, R], keys: Keys.Aux[R, K],
    ktl: hlist.ToList[K, Symbol]): Cpo[T]
}

但我只能得到字段的名称.

but I only can get field's name.

Zlaja

推荐答案

尝试

object typeablePoly extends Poly1 {
  implicit def default[A](implicit typeable: Typeable[A]): Case.Aux[A, String] = at(_ => typeable.describe)
}

trait Cpo[T] {

  def withPrimaryKey[R <: HList, K <: HList, V <: HList, V1 <: HList](f: Seq[Symbol] => Seq[Symbol])(implicit
    labellGeneric: LabelledGeneric.Aux[T, R],
    keys: Keys.Aux[R, K],
    ktl: hlist.ToList[K, Symbol],
    values: Values.Aux[R, V],
    mapper: hlist.Mapper.Aux[typeablePoly.type, V, V1],
    vtl: hlist.ToList[V1, String]
  ): Cpo[T] 
}

现在 ktl 给出字段名称列表(如 Symbols)，vtl 给出字段类型列表(如 Strings).

Now ktl gives list of field names (as Symbols) and vtl gives list of field types (as Strings).

试试

  object typeablePoly extends Poly1 {
    implicit def default[A](implicit typeable: Typeable[A]): Case.Aux[A, String] = at(_ => typeable.describe)
  }

  object nullPoly extends Poly0 {
    implicit def default[A]: ProductCase.Aux[HNil, A] = at(null.asInstanceOf[A])
  }

  trait Cpo[T] {

    def withPrimaryKey[R <: HList, K <: HList, V <: HList, V1 <: HList](f: Seq[Symbol] => Seq[Symbol])(implicit
      labellGeneric: LabelledGeneric.Aux[T, R],
      keys: Keys.Aux[R, K],
      ktl: hlist.ToList[K, Symbol],
      values: Values.Aux[R, V],
      mapper: hlist.Mapper.Aux[typeablePoly.type, V, V1],
      fillWith: hlist.FillWith[nullPoly.type, V],
      vtl: hlist.ToList[V1, String]
    ): Cpo[T] = {
      println(ktl(keys())) // List('i, 's)
      println(vtl(mapper(fillWith()))) // List(Int, String)
      ???
    }
  }

  case class MyClass(i: Int, s: String)
  new Cpo[MyClass] {}.withPrimaryKey(identity)

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