Support deriving Encoder / Decoder for `NamedTuples` ? #2326

Quafadas · 2024-11-08T12:39:26Z

Here's the (trivial) example...

  val nt: (name: String, age: Int) = (name = "Simon", age = 40)

  given fooDecoder1: Decoder[Foo] =
    deriveDecoder[(name: String, age: Int)]

and it's error

[{
	"resource": "/Users/simon/Code/namedTupleTest/nt.scala",
	"owner": "_generated_diagnostic_collection_name_#3",
	"code": "172",
	"severity": 8,
	"message": "No given instance of type scala.deriving.Mirror.Of[(name : String, age : Int)] was found for parameter A of method deriveDecoder in object semiauto. Failed to synthesize an instance of type scala.deriving.Mirror.Of[(name : String, age : Int)]:\n\t* class Any is not a generic product because it is not a case class\n\t* class Any is not a generic sum because it is not a sealed class",
	"source": "bloop",
	"startLineNumber": 31,
	"startColumn": 44,
	"endLineNumber": 31,
	"endColumn": 44
}]

With I guess the (slightly tedious?) workaround;

  given fooDecoder1: Decoder[(name: String, age: Int)] =
    new Decoder[(name: String, age: Int)] {
      def apply(c: HCursor): Decoder.Result[(name: String, age: Int)] =
        for {
          name <- c.downField("name").as[String]
          age <- c.downField("age").as[Int]
        } yield (name, age)
    }

  given fooEncoder1: Encoder[(name: String, age: Int)] =
    new Encoder[(name: String, age: Int)] {
      def apply(a: (name: String, age: Int)): Json =
        Json.obj(
          "name" -> Json.fromString(a.name),
          "age" -> Json.fromInt(a.age)
        )
    }

The text was updated successfully, but these errors were encountered:

jilen · 2024-12-19T08:47:55Z

There is a generic implementaion
https://scastie.scala-lang.org/JLAz8i1CTaqtvyblPvlOEA

MartinHH · 2025-03-07T17:33:22Z

Just pointing out the more more or less obvious here: the general problem with library support for named tuples is: library authors are encouraged to publish for LTS scala versions (currently: 3.3.x) "unless your library is built around some new language feature available only on Next". So to add such support, there would be three options:

wait until a new LTS version (>3.6.x) is out
do not follow the official recommendations and up the scala version to 3.6.x (seems like a bad idea)
publish the specific feature in a deficated 3.6.x-module while the rest of the library remains on 3.3.x

mzuehlke · 2025-03-09T11:59:05Z

The next LTS will likely be release in Q4 2025.
So no too far in the future.

Quafadas changed the title ~~Support NamedTuples ?~~ Support deriving Encoder / Decoder for NamedTuples ? Nov 8, 2024

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Support deriving Encoder / Decoder for `NamedTuples` ? #2326

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Support deriving Encoder / Decoder for NamedTuples ? #2326

Support deriving Encoder / Decoder for NamedTuples ? #2326

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Support deriving Encoder / Decoder for `NamedTuples` ? #2326

Support deriving Encoder / Decoder for `NamedTuples` ? #2326