Parsing primitive types in Circe

Question

I'm having an issue with json parsing when field can have different primitive value types. For example, I can get json:

{
  "name" : "john",
  "age" : 31
}

Or it can be in this form:

{
  "name" : "john",
  "age" : "thirty one"
}

Or in this way:

{
  "name" : "john",
  "age" : 31.0
}

I want to be able to parse field age to the following ADTs instances:

sealed trait PrimitiveWrapper

case class IntWrapper(v: Int) extends PrimitiveWrapper

case class StringWrapper(v: String) extends PrimitiveWrapper

case class FloatWrapper(v: Float) extends PrimitiveWrapper

So at the end I can get something like this:

case class Person(name: String, age: PrimitiveWrapper)

How can I do this? I found this topic: How to decode an ADT with circe without disambiguating objects

But in that solution we are parsing not primitive fields.

Answer 1

This is how you can do:

import cats.syntax.functor._
import io.circe.Decoder, io.circe.generic.auto._

sealed trait PrimitiveWrapper

case class IntWrapper(v: Int) extends PrimitiveWrapper

case class StringWrapper(v: String) extends PrimitiveWrapper

case class FloatWrapper(v: Float) extends PrimitiveWrapper

case class Person(name: String, age: PrimitiveWrapper)

object GenericDerivation {

  implicit val decodePrimitiveWrapper: Decoder[PrimitiveWrapper] =
    List[Decoder[PrimitiveWrapper]](
      Decoder.decodeInt.map(IntWrapper).widen,
      Decoder.decodeString.map(StringWrapper).widen,
      Decoder.decodeFloat.map(FloatWrapper).widen
    ).reduceLeft(_ or _)


  def main(args: Array[String]): Unit = {
    import io.circe.parser.decode
    println(decode[Person]("""{"name" : "john", "age" : 31 }"""))
    println(decode[Person]("""{"name" : "john", "age" : "thirty one" }"""))
    println(decode[Person]("""{"name" : "john", "age" : 31.3 }"""))
    // Prints
    // Right(Person(john,IntWrapper(31)))
    // Right(Person(john,StringWrapper(thirty one)))
    // Right(Person(john,FloatWrapper(31.3)))
  }
}

Note: The following get parse using an IntWrapper

 println(decode[Person]("""{"name" : "john", "age" : 31.0 }"""))

Update: As @Travis pointed out the decodePrimitiveWrapper can be written like this:

  implicit val decodePrimitiveWrapper: Decoder[PrimitiveWrapper] =
      Decoder.decodeInt.map(IntWrapper).widen[PrimitiveWrapper] or
        Decoder.decodeString.map(StringWrapper).widen[PrimitiveWrapper] or
        Decoder.decodeFloat.map(FloatWrapper).widen[PrimitiveWrapper]