How to assert length two array or value for field?

[John Ky]

Hi Everyone,

Is there a way to assert that the length of an array is two when decoding?

Or that a field in a Json object has a particular value?

Cheers,

-John

  Sydney, Australia

        

[John Ky]

Hello,

Thanks to Mark earlier on the tip with the validate method.

I'd like to ask a stylistic question.  I have a decoder that decodes [1, "s"] into 1 second, [2, "ns"] into 2 nanosecond, and fails to decode if the array is the wrong length or if the unit string is not recognised.  I currently interpret the unit string with a pattern match on DecodeResult.  Is this the most stylistically optimal way to express this behaviour in a decoder?  Code below.

Cheers,

-John

import argonaut._

import argonaut.Argonaut._

import scala.concurrent.duration._

import scalaz.{-\/, \/, \/-}

trait DurationDecoder {

  implicit def argoDecodeDuration: DecodeJson[FiniteDuration] = {

    DecodeJson { c =>

      for {

        number <- (c =\ 0).as[Long]

        duration <- {

          val cc = (c =\ 1)

          (cc.as[String] match {

            case DecodeResult(\/-(unit)) =>

              unit match {

                case "d"  => DecodeResult.ok(number days)

                case "h"  => DecodeResult.ok(number hours)

                case "m"  => DecodeResult.ok(number minutes)

                case "s"  => DecodeResult.ok(number seconds)

                case "ms" => DecodeResult.ok(number milliseconds)

                case "us" => DecodeResult.ok(number microseconds)

                case "ns" => DecodeResult.ok(number nanoseconds)

                case _    => DecodeResult.fail(s"Invalid duration unit '$unit'", cc.history)

              }

            case failure => DecodeResult.fail(s"Expected duration unit", cc.history)

          })

        }

      } yield duration

    }.validate({ c => (c =\ 2).failed }, "Too many elements for duration")

  }

}

object DurationCodec extends DurationCodec