无形对齐与不同类型但相同的标签答案

【问题标题】：Shapeless align with different types but same labels无形对齐与不同类型但相同的标签
【发布时间】：2017-08-24 14:06:40
【问题描述】：

当两条记录具有相同的字段名称但不同的值时，是否有人知道如何对齐它们一个值包含在 Column 中，另一个包含在 Option 中，我需要对齐它们，因为顺序不同

import shapeless._
import shapeless.labelled.{FieldType, field}
import shapeless.ops.hlist.{Align, ToTraversable, ZipWith}

object ShapelessTest {


  def zipClasses[A, B, P <: Poly2, ARepr <: HList, BRepr <: HList, R <: HList, X]
  (a: A, b: B, f: P)(
    implicit
    aGen : LabelledGeneric.Aux[A, ARepr],
    bGen : LabelledGeneric.Aux[B, BRepr],
//    align : Align[ARepr, BRepr],
    zipWith : ZipWith.Aux[ARepr, BRepr, P, R],
    toTrav: ToTraversable.Aux[R, List, X]
  ): List[X] =
    aGen.to(a).zipWith(bGen.to(b))(f).toList
//    align.apply(aGen.to(a)).zipWith(bGen.to(b))(f).toList



  def main(args: Array[String]): Unit = {


    case class Column[A](value: A)

    case class DTable(id: Column[Long], s2: Column[Int], s: Column[String])
    case class DFilter(id: Option[Long], s: Option[String], s2: Option[Int])

    object filter extends Poly2 {
      implicit def repr[K <: Symbol, V] = at[FieldType[K, Column[V]], FieldType[K, Option[V]]] { (a, b) =>
        field[K]( (a, b).asInstanceOf[(Any, Any)] )
      }
    }

    val dTable = new DTable(Column(1L), Column(3), Column("s"))
    val dFilter = new DFilter(Option(222L), Option("second"), Option(234))


//    def filter[A](col: Column[A], filterCriteria: Option[A]): Option[Boolean] = ???

//    def filterClass(table: DTable, filter: DFilter): List[Option[Boolean]] = ???
    def filterClass(t: DTable, f: DFilter): List[(Any, Any)] = zipClasses(t, f, filter)

    val res = filterClass(dTable, dFilter)
    println(res)

  }

}

我可以对齐具有完全相同类型的两条记录，并且即使类型不精确但它们需要通过键对齐，我也可以对两条记录执行 zipWith。

谢谢

【问题讨论】：

标签： scala shapeless labelled-generic

【解决方案1】：

如果我们忽略字段名称的相似性并专注于类型，我们可以执行以下操作：

    def alignRecordByTypeInsideConstructor[A, B, L1 <: HList, L2 <: HList,
      F[_], G[_], L3 <: HList, L4 <: HList, Out <: HList](a: A, b: B, f: F ~> Id, g: Id ~> G)(
      implicit
      gen1: Generic.Aux[A, L1],
      gen2: Generic.Aux[B, L2],
      comapped1: Comapped.Aux[L1, F, L3],
      natTRel1: NatTRel[L1, F, L3, Id],
      comapped2: Comapped.Aux[L2, G, L4],
      natTRel2: NatTRel[L2, G, L4, Id],
      align: Align[L3, L4],
      mapped: Mapped.Aux[L4, G, Out],
      natTRel3: NatTRel[L4, Id, Out, G]
    ): Out =
      alignByTypeInsideConstructor[L1, L2, F, G, L3, L4, Out](gen1.to(a), gen2.to(b), f, g)

    def alignByTypeInsideConstructor[L1 <: HList, L2 <: HList,
      F[_], G[_], L3 <: HList, L4 <: HList, Out <: HList](l1: L1, l2: L2, f: F ~> Id, g: Id ~> G)(
      implicit
      comapped1: Comapped.Aux[L1, F, L3],
      natTRel1: NatTRel[L1, F, L3, Id],
      comapped2: Comapped.Aux[L2, G, L4],
      natTRel2: NatTRel[L2, G, L4, Id],
      align: Align[L3, L4],
      mapped: Mapped.Aux[L4, G, Out],
      natTRel3: NatTRel[L4, Id, Out, G]): Out =
      natTRel3.map(g, align(natTRel1.map(f, l1)))

    object columnToId extends (Column ~> Id) {
      override def apply[A](column: Column[A]): A = column match {
        case Column(a) => a
      }
    }

    object idToOption extends (Id ~> Option) {
      override def apply[A](a: A): Option[A] = Some(a)
    }

    alignByTypeInsideConstructor(
      Column(1L) :: Column(2) :: Column("a") :: HNil,
      Option(3L) :: Option("b") :: Option(4) :: HNil,
      columnToId,
      idToOption
    )

  //Some(1) :: Some(a) :: Some(2) :: HNil

    alignRecordByTypeInsideConstructor(
      DTable(Column(1L), Column(2), Column("a")),
      DFilter(Option(3L), Option("b"), Option(4)),
      columnToId,
      idToOption
    )

  //Some(1) :: Some(a) :: Some(2) :: HNil

【讨论】：