allow selectDynamic to have optional type parameter - unified with type of field

[Katrix]

Compiler version

3.1.0

Minimized code

trait TC[A] {
  def cast(any: Any): A
}
object TC {
  given TC[Int] with {
    override def cast(any: Any): Int = any.asInstanceOf[Int]
  }
  given TC[String] with {
    override def cast(any: Any): String = any.asInstanceOf[String]
  }
}

class DiscordRecord(private val map: Map[String, Any]) extends Selectable {
  def selectDynamic[A](name: String)(using decoder: TC[A]): A =
    decoder.cast(map(name))
}

type Test = DiscordRecord {
  val foo: Int
}

val t: Test = ???
t.foo

Output

[error] -- Error: D:\DevProjects\Incubating\AckCordNext\src\main\scala\ackcordnext\data\datamodel\userideas\userideas.scala:260:7
[error] 260 |  t.foo
[error]     |       ^
[error]     |ambiguous implicit arguments: both object given_TC_Int in object TC and object given_TC_String in object TC match type ackcordnext.data.datamodel.userideas.Idea5.TC[A] of parameter decoder of method selectDynamic in class DiscordRecord

Expectation

I would expect selectDynamic getting the type of the field, and thus finding the typeclass associated with it.

[bishabosha]

Am I right in suggesting that you want A in def selectDynamic[A] to be substituted with the return type of the field?

[Katrix]

Yes. That's the gist of it.

[bishabosha]

I don't know how hard this would be to implement internally, but I think it's worth a SIP - with some more motivating use cases

[Katrix]

I'll try to write something up eventually