[spray-json] Cannot deserialize a generic collection

[Anatoly Rabinovich]

Hi,

I'm trying to deserialize a json string into a generic collection.

My code looks something like this:

class MyClass(json: String) {
  def collectionType1: Set[Type1] = loadElements[Type1]

  def collectionType2: Set[Type2] = ???

  private def loadElements[T]: Set[T] = {
    json.parseJson.convertTo[Set[T]]
  }
}

I also have the following defined (I have the exact same definition for 'Type2', the case class looks different):

case class Type1(p1: String, p2: String)

object Type1JsonProtocol extends DefaultJsonProtocol {
  private implicit val collectionType1Format = jsonFormat2(Type1)

  implicit object Type1SetJsonReader extends JsonReader[Set[Type1]] {
    override def read(json: JsValue): Set[Country] = json match {
      case JsArray(elements) => elements.map(_.convertTo[Type1]) toSet
      case x => deserializationError("Expected Collection as JsArray, but got " + x)
    }
  }
}

When compiling the code, I get the following error:

Error:(25, 29) Cannot find JsonReader or JsonFormat type class for Set[T]

    val res = json.convertTo[Set[T]]

                            ^

and:

Error:(25, 29) not enough arguments for method convertTo: (implicit evidence$1: spray.json.JsonReader[Set[T]])Set[T].

Unspecified value parameter evidence$1.

    val res = json.convertTo[Set[T]]

                            ^

I'm obviously missing something, but have a feeling it's something small. Does anyone have any clue?

Thanks!

[Anatoly Rabinovich]

I've also posted this question on stack overflow: https://stackoverflow.com/questions/34204153/cannot-deserialize-a-generic-collection