Question

我有以下内容：

sealed trait baseData {
  def weight: Int
  def priority: Int
} 

sealed trait moreData {
  def weight: Int
  def priority: Int
  def t: String
  def id: String
} 

case class data1(override val weight: Int, override val priority: Int) extends baseData 
case class moreData1 (override val weight:Int, override val priority: Int, override val t: String, override val id: String)extends moreData

我正在从案例类中生成HLists：

val h1 = LabelledGeneric[data1].to(data1(1,2))
val h2 = LabelledGeneric[moreData1].to(moreData1(3,4,"a","b"))

如何修剪或过滤h2，使其仅包含h1中的字段？我觉得我需要类似val filtered = h2.foldRight(HNil)(keepFunc)的东西，但却无法弄清楚如何写keepFunc。有任何想法吗？

Answer 1

您可以根据键进行过滤。代码不是通用的，但希望足以说明这个概念。

val gen1 = LabelledGeneric[data1]
val gen2 = LabelledGeneric[moreData1]

val h1 = gen1.to(data1(1,2))
val h2 = gen2.to(moreData1(3,4,"a","b"))

val keys1 = Keys[gen1.Repr].apply
val keys2 = Keys[gen2.Repr].apply

object pair extends Poly2 {
  implicit def default[T, U] = at[T, U]((_, _))
}

object keep extends Poly2 {
  implicit def keepFunc[T, K, L <: HList] =
    at[(T, K), L] { case ((t, key), l) =>
      if (keys1.toList.contains(key)) t :: l else l
    }
}

val filtered = h2.zipWith(keys2)(pair).foldRight(HNil)(keep)

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1 个答案: