Clarifying nested object conversion

I’m trying to understand how I can achieve the following:

sealed trait TC
case class ITC(count:Int, work:TC) extends TC
case class SSTC(query:String, args:List[AnyRef]) extends TC

case class Global(work:List[TC], runtime:Option[FiniteDuration)

I can’t seem to understand the process that would be required to achieve something like this. I get the exception listed in the documentation (i.e could not find implicit value for parameter conv: pureconfig.ConfigConvert[Global]) but I can’t for the life of me figure out what’s causing it or what steps I can use to fix it.

I’ve tried to create a custom converter, but I’m not sure how to leverage pureconfig to load the types it already knows about.

[melrief]

The error means that pureconfig cannot find the ConfigConvert instance for one or more types in Global and consequently it cannot derive the ConfigConvert for Global itself. Now the question is which type. There is a way to check the type by using a scala console. Basically you can check every type until you get an error

> import pureconfig.ConfigConvert
> ConfigConvert[Int]
res0: pureconfig.ConfigConvert[Int] = pureconfig.ConfigConvert$$anon$5@4737d730
> // Int has a ConfigConvert, no error
> ConfigConvert[String]
res1: pureconfig.ConfigConvert[String] = pureconfig.ConfigConvert$$anon$5@1683a9f5
> // same for String
> ConfigConvert[FiniteDuration]
res2: pureconfig.ConfigConvert[FiniteDuration] = pureconfig.ConfigConvert$$anon$6@489b26b1
> // same for FiniteDuration...
> ConfigConvert[AnyVal]
<console>:17: error: could not find implicit value for parameter conv: pureconfig.ConfigConvert[AnyVal]
       ConfigConvert[AnyVal]
> // ...but not for AnyVal! The issue is AnyVal

The issue is that AnyVal doesn’t have a ConfigConvert because it’s an abstract class and not a sealed family. The good news is that AnyVal contains all types that can easily be converted from/to String and it should be easy to implement a ConfigConverter for it. Scala defines nine types that are subclasses of AnyVal, which are Double, Float, Long, Int, Char, Short, Byte, Unit and Boolean. pureconfig has ConfigConvert instances for Double, Float, Long, Int, Short and Boolean. You can either decide to ignore the remaining types, which are Char, Byte and Unit, or create ConfigConvert for them. It’s up to you but here I’m going to ignore them and show how to create the ConfigConvert of AnyVal from existing ConfigConvert instances for the subclasses. The code that I’m going to use can be enhanced with the missing ConfigConvert instances. The code for AnyVal would be:

import com.typesafe.config.{ConfigFactory,ConfigValue}
import pureconfig._
import pureconfig.ConfigConvert._
import scala.util.Try

implicit val anyValConfigConvert: ConfigConvert[AnyVal] = new ConfigConvert[AnyVal] {

  def from(cv: ConfigValue): Try[AnyVal] =
      ConfigConvert[Double].from(cv) orElse
      ConfigConvert[Int].from(cv)    orElse
      ConfigConvert[Long].from(cv)   orElse
      ConfigConvert[Float].from(cv)  orElse
      ConfigConvert[Short].from(cv)  orElse
      ConfigConvert[Boolean].from(cv)

  def to(a: AnyVal): ConfigValue = ???
}

Now that there is an instance of ConfigConvert for AnyVal, pureconfig can derive Global:

> val config = ConfigFactory.parseString(
      """{
        | work: [
        |   { type: "sstc",
        |     query: "na",
        |     args: [ 1, 2.4, "3", false ]
        |    }
        | ],
        | runtime: 1s
        |}""".stripMargin)
> println(loadConfig[Global](config))
Success(Global(List(SSTC(na,List(1.0, 2.4, 3.0, false))),Some(1 second)))

[sidhant92]

@melrief What workaround has been found for this? Im having the same issue. My Nested Case Classes is not compiling. Its not related to AnyVal.