👀 Views: 74 💬 Answers: 1 📅 Created: 2025-08-27

scala akka-streams implicits type-classes Scala

I've been working on this all day and I've been banging my head against this for hours. I'm currently working on a project using Scala 2.13 and Akka Streams, and I've run into a frustrating scenario involving implicits and type classes. I'm trying to create a custom `Flow` that processes elements of a specific type, leveraging a type class instance to perform transformations. However, I'm getting the following behavior: `Could not find implicit value for parameter transformer: Transformer[A]`. Here’s what I have so far: ```scala import akka.stream.scaladsl.{Flow, Sink, Source} import scala.concurrent.ExecutionContext.Implicits.global trait Transformer[A] { def transform(a: A): String } object Transformer { implicit val stringTransformer: Transformer[String] = new Transformer[String] { def transform(a: String): String = a.toUpperCase } implicit val intTransformer: Transformer[Int] = new Transformer[Int] { def transform(a: Int): String = (a * 2).toString } } def processFlow[A](implicit transformer: Transformer[A]): Flow[A, String, _] = { Flow[A].map(transformer.transform) } val source = Source(List("hello", "world", 1, 2)) val flow = processFlow[String] // This should use stringTransformer source.via(flow).runWith(Sink.foreach(println)) ``` The scenario seems to stem from how I'm trying to call `processFlow`. When I call `processFlow[String]`, it works fine, but if I try to call it with a mixed type source like `List("hello", "world", 1, 2)`, Scala want to infer the implicit `Transformer`. I’ve tried defining a `Flow[Any]`, but that results in type safety issues during the transformation. How can I make this code work with mixed types in the source while still utilizing the implicits properly? Am I missing something in the type inference or implicits resolution here? Any help would be appreciated! The project is a CLI tool built with Scala. The project is a service built with Scala.