Scala structural type dependency injection between modules

api.scala

// This file is assumed to be in the API module

// =======================
// service interfaces
trait OnOffDevice {
  def on: Unit
  def off: Unit
}
trait SensorDevice {
  def isCoffeePresent: Boolean
}

// =======================
// service implementations
class Heater extends OnOffDevice {
  def on = println("heater.on")
  def off = println("heater.off")
}
class PotSensor extends SensorDevice {
  def isCoffeePresent = true
}

// =======================
// service declaring two dependencies that it wants injected,
// is using structural typing to declare its dependencies
class Warmer(env: {
  val potSensor: SensorDevice
  val heater: OnOffDevice
}) {
  def trigger = {
    if (env.potSensor.isCoffeePresent) env.heater.on
    else env.heater.off
  }
}

trait Config {
  lazy val potSensor:SensorDevice
  lazy val heater:OnOfDevice
  lazy val warmer:Warmer
}

//for simplicity there is no error handling
object CodecRepository {
  var config:Config = null
}

Server.scala

//This file is assumed to be in the server module

class ConfigImpl extends Config {
  lazy val potSensor = new PotSensor
  lazy val heater = new Heater
  lazy val warmer = new Warmer(this) // this is where injection happens
}

CodecConfig.config = new ConfigImpl

// following part can be in plugin as well
class Client(env : { val warmer: Warmer }) {
  env.warmer.trigger
}

new Client(CodecConfig.config)