Named tuples and json

tuples-json.scala

import io.circe.*
import literal.*
import cats.implicits.*
import NamedTuple.NamedTuple
import language.experimental.namedTuples

@main
def greet =
  type Person = (name: String, age: Int)
  val greeting = json"""{"name": "Joe", "age": 42}"""
    .as[Person]
    .map(p => s"Hello, ${p.name}, you reached ${p.age}")
  println(greeting)

// ------- Impl ------

class NamedTupleDecoder[Names <: Tuple, Values <: Tuple](data: Seq[(String, Decoder[?])])
    extends Decoder[NamedTuple[Names, Values]]:
  override def apply(c: HCursor): Decoder.Result[NamedTuple[Names, Values]] =
    data
      .map((name, decoder) => c.downField(name).as(using decoder))
      .sequence
      .map(vals => NamedTuple.build()(Tuple.fromArray(vals.toArray).asInstanceOf[Values]))
end NamedTupleDecoder

inline given decodeNamedTuple[Names <: Tuple, Vals <: Tuple]
    : Decoder[NamedTuple.NamedTuple[Names, Vals]] =
  val decoders        = compiletime.summonAll[Tuple.Map[Vals, Decoder]]
  val names           = compiletime.constValueTuple[Names].toList.asInstanceOf[List[String]]
  val untypedDecoders = decoders.toList.asInstanceOf[List[Decoder[?]]]
  NamedTupleDecoder(names.zip(untypedDecoders))