Macro to resolve Companion depending Classpath (Maven-Profile)

lostiniceland · October 15, 2019, 4:44pm

I am testing out some Metrics-providers (namely Kamon and Micrometer) which I separated by two dedicated Maven profiles. Depending on the activated profile the corresponding companion object should be resolved (they share the same trait)-

First I tried to resolve the companion via standard Java reflection but this seems to be more difficult than expected. Now, I’ve read that Macros can actually help in situations like this at compile time.
Can someone point me to a documentation for Scala 2.13 which describes Macros? I’ve also read in the past that they are supposed to be deprecated but obviously have returned.

Thanks

Jasper-M · October 15, 2019, 6:05pm

I once wrote a little macro for that. I guess it should still work.

gist.github.com

https://gist.github.com/Jasper-M/1b6540fecfa3af9094dab1614038a1b5

HasCompanion.scala

import scala.language.experimental.macros
import scala.reflect.macros.whitebox.Context

trait HasCompanion[A] {
  type Type
  def companion: Type
}
object HasCompanion {
  type Aux[A,C] = HasCompanion[A] { type Type = C }
  def apply[A](implicit hc: HasCompanion[A]): hc.type = hc

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lostiniceland · October 16, 2019, 7:44am

Thanks for the gist.
Since I am quite new to Scala, I am a little overwhelmed by the types there. Could you give a little advice how to use the macro?