Configuration for Akka application ref: http://qiita.com/mather314/items/a3cd9dd1f3c4cfea6fbf

file0.scala

import akka.actor.{ExtendedActorSystem, Extension, ExtensionId}

class SampleExtentionImpl(system: ExtendedActorSystem) extends Extension {
  val hoge = "HOGE"
}

object SampleExtension extends ExtensionId[SampleExtensionImpl] {
  def createExtension(system: ExtendedActorSystem) = new SampleExtensionImpl(system)
}

file1.scala

import akka.actor.Actor

class SampleActor extends Actor {
  val ext = SampleExtension(system)

  def hoge = ext.hoge //=> "HOGE"
}

file2.scala

import com.typesafe.config.Config
import akka.actor.ActorSystem

// configを定義するtrait
trait ConfigSupplier {
  val config: Config
}

// configから読み込む設定情報の実装
trait DatabaseSetting { this: ConfigSupplier =>
  import scala.util.Try
  val dbHost = Try(config.getString("sample.db.host")).getOrElse("localhost")
  val dbPort = Try(config.getInt("sample.db.port")).getOrElse(5432)
}

// 設定情報を利用するクラス
class SampleApplication { this: DatabaseSetting =>
  val connection = getConnection(dbHost, dbPort)
}

object Main extends App {
  val system = ActorSystem()

  // インスタンス化のときに配線と注入
  val app = new SampleApplication with DatabaseSetting with ConfigSupplier {
    val config = system.settings.config
  }

  //...
}