Type class for container type - scala

Question

I want to build an interface that doesn't have any dependencies, only scala library
Let's imagine this is what i want:
iface.jar
trait jsonIface[JsValue] {
def turnJsonIntoClass[T](t: JsValue)
}
As you see it doesn't contains any imports.
Let's go to implementation:
iface_implementation1.jar
import play.api.libs.json._
trait myPlayJsonImpl extends jsonIface[JsValue] {
def turnJsonIntoClass[T](t: JsValue) { t.as[T] }
}
But this wouldn't compile because as[T] needs implicit Reads[T]
So i rewrote my iface like that:
trait jsonIface[JsValue] {
type metaInfo[T]
def turnJsonIntoClass[T](t: JsValue)(implicit meta: metaInfo[T])
}
and play json impl looks like that:
import play.api.libs.json._
trait myPlayJsonImpl extends jsonIface[JsValue] {
type conv[M] = Reads[M]
def turnJsonIntoClass[T](t: JsValue)(implicit reads: Reads[T]) { t.as[T] }
}
and json4s looks like that:
import org.json4s.JsonAST._
trait json4sImpl extends jsonIface[JValue] {
type conv[M] = Manifest[M]
def turnJsonIntoClass[T](t: JsValue)(implicit reads: Manifest[T]) { t.extract[T] }
}
This compiles but it looks cumbersome

Answer 1

Normally when you start to work with type-class traits you continue to do so rather than work with OOP traits:
import org.json4s.Formats
import org.json4s.JsonAST.JValue
import play.api.libs.json.{JsValue, Reads}
trait jsonIface[JsValue, T] {
def turnJsonIntoClass(t: JsValue): T
}
object jsonIface {
implicit def json4sImpl[T](implicit formats: Formats, manifest: Manifest[T]): jsonIface[JValue, T] = new jsonIface[JValue, T] {
def turnJsonIntoClass(t: JValue): T = t.extract[T]
}
implicit def myPlayJsonImpl[T](implicit reads: Reads[T]): jsonIface[JsValue, T] = new jsonIface[JsValue, T] {
def turnJsonIntoClass(t: JsValue): T = t.as[T]
}
}
or
object jsonIface {
implicit def json4sImpl[T](implicit formats: Formats, manifest: Manifest[T]): jsonIface[JValue, T] = (t: JValue) => t.extract[T]
implicit def myPlayJsonImpl[T](implicit reads: Reads[T]): jsonIface[JsValue, T] = (t: JsValue) => t.as[T]
}