Simple Pipeline demo (a pipeline MUST start with a generator, folllowed by 0 to many transformers and MUST end with a serializer).

gistfile1.scala

trait PipelineComponent {
  def execute: Unit
}
trait Generator extends PipelineComponent {
  override def execute: Unit = print("Generator executing\n")
}
trait Transformer extends PipelineComponent {
  override def execute: Unit = print("Transformer executing\n")
}
trait Serializer extends PipelineComponent {
  override def execute: Unit = print("Serializer executing\n")  
}

abstract class AbstractPipeline(pipelineComponents: List[PipelineComponent]) 

case class EmptyPipeline extends AbstractPipeline(List()) {
   def add(generator: Generator): NonEmptyPipeline = new NonEmptyPipeline(List(generator))
}

case class NonEmptyPipeline(pipelineComponents: List[PipelineComponent]) extends AbstractPipeline(pipelineComponents) {
  def add(transformer: Transformer): NonEmptyPipeline = new NonEmptyPipeline(pipelineComponents :+ transformer)
  def add(serializer: Serializer): FinishedPipeline = new FinishedPipeline(pipelineComponents :+ serializer)
}

case class FinishedPipeline(pipelineComponents: List[PipelineComponent]) extends AbstractPipeline(pipelineComponents) {
  def execute(): Unit = pipelineComponents.foreach(_.execute)
}

/**
object PipelineApp extends App {
  val generator = new Object with Generator
  val transformer1 = new Object with Transformer
  val transformer2 = new Object with Transformer 
  val serializer = new Object with Serializer
  new EmptyPipeline().add(generator).add(transformer1).add(transformer2).add(serializer).execute 
}  
  
this will print: 

Generator executing
Transformer executing
Transformer executing
Serializer executing
**/