Scala DI exploration.scala

trait PaymentComponent {
  val paymentService: PaymentService
  trait PaymentService {def pay(what: String) }
}

trait PaypalPaymentService  extends PaymentComponent {
  override val paymentService:PaymentService = new PaypalImpl 
  class PaypalImpl extends PaymentService {
      def pay(what: String) = println("Paypal payment for "+what)
  }
}

trait CyberSourcePaymentService  extends PaymentComponent {
  override val paymentService:PaymentService = new CyberSourceImpl 
  class CyberSourceImpl extends PaymentService {
      def pay(what: String) = println("CyberSource payment for "+what+ " in "+this)
  }
}

trait ServiceWithPaymentComponent extends PaymentComponent {
  val depService: ServiceWithPayment
  
  trait ServiceWithPayment {
    def impl:String // Abstract, must implement
    def doit = {println("Doing it with "+impl+" and paying it"); paymentService.pay(impl)}
  }
}

trait MyServiceWithPayment extends ServiceWithPaymentComponent with PaymentComponent {
  override val depService = new MyServiceWithPaymentImpl
  class  MyServiceWithPaymentImpl extends ServiceWithPayment  {
    def impl = "MyDepImpl"
  }
}

trait Configuration extends CyberSourcePaymentService with MyServiceWithPayment {
}

trait MockConfiguration extends PaymentComponent with MyServiceWithPayment {
  class MockImpl extends PaymentService {
      def pay(what: String) = println("Mock payment for "+what+ " in "+this)
  }
  override val paymentService = new MockImpl
}

class MySnippet extends PaymentComponent with Configuration {
  def render = { println("Rendering my snippet"); paymentService.pay("my stuff")}
}

class YourSnippet extends PaymentComponent with ServiceWithPaymentComponent with Configuration {
  def render = {println("Rendering your snippet"); depService.doit }
}

object Scratch {
 def main(args : Array[String]) : Unit = {
   // Real config
   (new MySnippet).render
   (new YourSnippet).render
   
   // Do test
   (new MySnippet with MockConfiguration).render
  }
}