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Pattern matching on a simple lifeless HLIST

I wrote this simple code using the shapeless library

import shapeless.LabelledGeneric
case class Icecream(name: String, numberOfCherries: Int, inCone: Boolean)

object ShapelessRecordEx2 extends App {
   val gen = LabelledGeneric[Icecream]
   val hlist = gen.to(Icecream("vanilla", 2, false))
   hlist match {
      case h :: _ => println(h)
   }
}

But it doesn't even compile

Error:(12, 14) constructor cannot be instantiated to expected type;
 found   : scala.collection.immutable.::[B]
 required: shapeless.::[String with shapeless.labelled.KeyTag[Symbol with shapeless.tag.Tagged[String("name")],String],shapeless.::[Int with shapeless.labelled.KeyTag[Symbol with shapeless.tag.Tagged[String("numberOfCherries")],Int],shapeless.::[Boolean with shapeless.labelled.KeyTag[Symbol with shapeless.tag.Tagged[String("inCone")],Boolean],shapeless.HNil]]]
      case h :: _ => println(h)

This code would be fine if I was working with a regular list.

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1 answer


You just need import, by default scala.Predef

imports the statement ::

from scala.collection.immutable.List

.

import shapeless.LabelledGeneric
import shapeless.::
case class Icecream(name: String, numberOfCherries: Int, inCone: Boolean)

object ShapelessRecordEx2 extends App {
   val gen = LabelledGeneric[Icecream]
   val hlist = gen.to(Icecream("vanilla", 2, false))
   hlist match {
      case h :: _ => println(h)
   }
}


There is one more option to import ListCompat._

.

import shapeless.HList.ListCompat._

object ShapelessRecordEx2 extends App {
  val gen = LabelledGeneric[Icecream]
  val hlist = gen.to(Icecream("vanilla", 2, false))
  hlist match {
    case h #: _ => println(h)
  }
}
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