Scalar types (Int, Long, Float, Double, Boolean) as map keys

[OndrejSpanel]

Scalar types cannot be used as map keys when serializing to JSON, which I find inconvenient (I think Circe allows this). Quoting them as strings should be trivial. If you are not opposed to the idea, I can try preparing a PR.

[sirthias]

hmm... yes, I think there is no real risk in allowing for non-string, simple types as map keys, which get converted to their default toString results at the lowest-possible level.
The only change required would be in the JsonRenderer (plus a few extra test cases).

Sure, I'd be happy to merge your PR here, thank you!

[OndrejSpanel]

If anyone is interested, here is user space workaround (for Json only, Cbor does not need it):

https://gist.github.com/OndrejSpanel/bcae5a077fb7a72f232e12e828027aac

Core is:

  trait MapKeyCodec[K] {
    def keyToString(k: K): String
    def keyFromString(s: String): K
  }

  implicit def mapEncoder[K: MapKeyCodec: Encoder, T: Encoder]: Encoder[Map[K, T]] = Encoder { (w, value) =>
    if (w.writingCbor) { // any key type is fine on Cbor
      Encoder.forMap[K, T, Map].write(w, value)
    } else { // on Json we need string keys only
      val k = implicitly[MapKeyCodec[K]]
      val valueMap = value.map(kv => k.keyToString(kv._1) -> kv._2)
      Encoder.forMap[String, T, Map].write(w, valueMap)
    }
  }
  implicit def mapDecoder[K: MapKeyCodec : Ordering : Decoder, T: Decoder]: Decoder[Map[K, T]] = Decoder { r =>
    if (r.readingCbor) {
      Decoder.forMap[K, T].read(r)
    } else {
      val k = implicitly[MapKeyCodec[K]]
      val stringMap = Decoder.forMap[String, T].read(r)
      stringMap.map(kv => k.keyFromString(kv._1) -> kv._2)
    }
  }

[sirthias]

Thank you for this snippet, @OndrejSpanel, this is definitely a workable solution.