Scala -- Using multimaps

MultiMap.scala

    import scala.collection.mutable.{ Map, HashMap, Set, MultiMap }
    // val evictedModuleIDs: Seq[ModuleID] = ...
    val evicteds: Map[String, Set[ModuleID]] =
      (new HashMap[String, Set[ModuleID]] with MultiMap[String, ModuleID] /: evictedModuleIDs) {
        case (acc, m) =>
        val key = s"${m.organization}:${m.name}"
        acc.addBinding(key, m)
      }