Typeclass that provides evidence that a type has a companion object, and access to the object.

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
  implicit def mkHasCompanion[A,C]: Aux[A,C] = macro MacroHasCompanion.hasCompanionMacro[A]
}

object MacroHasCompanion {
  def hasCompanionMacro[A: c.WeakTypeTag](c: Context): c.Tree = {
    import c.universe._
    val aTpe = weakTypeOf[A]
    val companionTpe = aTpe.companion
    val companion = aTpe.typeSymbol.companion
    val HasCompanion = weakTypeOf[HasCompanion[A]]
    if (companionTpe =:= NoType)
      c.abort(c.enclosingPosition, s"No companion found for type $aTpe.")
    else if (!companion.isModule)
      c.abort(c.enclosingPosition, s"$aTpe is the companion.")
    else
      q"new $HasCompanion { type Type = $companionTpe; def companion = $companion }"
  }
}