Faster with much less memory consumption JSON object reader

gistfile1.scala

  def objectReader[T1,T2,T3,T4,R](t1: String, t2: String, t3: String, t4: String)(f: (T1,T2,T3,T4) => R)(implicit readsT1:Reads[T1], readsT2:Reads[T2], readsT3:Reads[T3], readsT4:Reads[T4]): Reads[R] = {

    def orElse[A](a:A, default: =>A) = if(a!=null) a else default

    Reads[R]{

      case JsObject(fields) =>

        var t1V:JsResult[T1] = null.asInstanceOf[JsResult[T1]]
        var t2V:JsResult[T2] = null.asInstanceOf[JsResult[T2]]
        var t3V:JsResult[T3] = null.asInstanceOf[JsResult[T3]]
        var t4V:JsResult[T4] = null.asInstanceOf[JsResult[T4]]

        var els = fields.toIterator
        while((els.hasNext) && (t1V == null || t2V == null || t3V == null || t4V == null)){

          val (key, value) = els.next()

          key match {

            case `t1` => t1V = readsT1.reads(value)

            case `t2` => t2V = readsT2.reads(value)

            case `t3` => t3V = readsT3.reads(value)

            case `t4` => t4V = readsT4.reads(value)

            case _ => //

          }
        }

        (t1V, t2V, t3V, t4V) match {

          case (JsSuccess(tt1, _), JsSuccess(tt2, _), JsSuccess(tt3, _), JsSuccess(tt4, _)) =>

            JsSuccess(f(tt1, tt2, tt3, tt4))

          case _ =>

            List(
              orElse(t1V, JsError(Seq((JsPath.\(t1), Seq(ValidationError("error.path.missing")))))),
              orElse(t2V, JsError(Seq((JsPath.\(t2), Seq(ValidationError("error.path.missing")))))),
              orElse(t3V, JsError(Seq((JsPath.\(t3), Seq(ValidationError("error.path.missing")))))),
              orElse(t4V, JsError(Seq((JsPath.\(t4), Seq(ValidationError("error.path.missing"))))))
            ).collect { case e: JsError => e }.reduceLeft(_.++(_))

        }

      case js => JsError(Seq(JsPath() -> Seq(ValidationError("error.expected.jsobject"))))

    }
  }

Good point. I'm not a big fan of the solution though, as you may have expected ;)

A definition of JsObject along the line of case class JsObject(fields: Map[String, JsValue]) would be much more appropriate in your case.

It used to be so, except you'd loose the original order of fields :)

I know. There's no "good" solution :(