the_cake_is_a_lie.scala

trait ConfigComponent {
  trait Config {
    def get[T](key: String): T
  }
  
  val config: Config
}

trait ConfigComponentImpl extends ConfigComponent {
  class ConfigImpl extends Config {
    val values = Map[String, Any]("some.key" -> 42)
    
    def get[T](key: String) = values(key).asInstanceOf[T]
  }
  
  val config = new ConfigImpl
}

the_cake_is_a_lie2.scala

trait NetServiceComponent {
  type NetSession <: NetSessionInterface
  val netService: NetServiceInterface
  
  trait NetServiceInterface {
    type TFut = Future[this.type]
    
    def connected: Seq[NetSession]
    
    def boot(): TFut
    def kill(): TFut
  }
  
  trait NetSessionInterface {
    type TFut = Future[this.type]
    
    def service: NetService
    
    def write(o: Any): TFut
    def flush(): TFut
    def close(): TFut
  }
}

trait NetServiceComponentImpl { self: ConfigurationComponent =>
  private val port = config.get("port"): Int
  
  type NetSession = NetSessionImpl
  val netService = new NetServiceImpl

  class NetServiceImpl extends NetService {
    val connected = mutable.ArrayBuffer.empty[NetSession]
    
    def boot(): TFut = ???
    def kill(): TFut = ???
  }
  
  class NetSessionImpl extends NetSessionInterface {
    def service = netService
    
    def write(o: Any) = ???
    def flush() = ???
    def close() = ???
  }
}