Parameter to the Trait in scala

Question

I need a trait with takes a parameter and uses it for creation of implicit object. In the following way.

trait SparkSessionTrait(name:String) {

  implicit val sparkSession = SparkSession
                                .builder()
                                .appName("AcoE Workflow_${name}")
                                .master("yarn")
                                .enableHiveSupport()
                                .getOrCreate()
}

How can i pass the args(0) as a parameter to the SParkSessionTrait

We can do if it is a case class but in my case it is an Object

object Test extends SparkSessionTrait{




  def main(args: Array[String]): Unit = {
    val name = args(0)


    sparkSession.catalog.clearCache()
}

Answer 1

The way you want to do it simply doesn't make sense.

trait SparkSessionTrait(name:String)

isn't allowed (but will be in Scala 3 with some limitations), it needs to be a class .

But the more important issue is that if you extend a class with parameters (or trait in Scala 3, that doesn't matter), these parameters need to be known at construction time. Ie you must have object Text extends SomeSessionTrait(someName) . By the time main method is called, it's far too late, you can't set name from there.

One way to change the program and make it compile is

class SparkSessionTrait(name:String) {
  implicit val sparkSession = SparkSession
                                .builder()
                                .appName("AcoE Workflow_${name}")
                                .master("yarn")
                                .enableHiveSupport()
                                .getOrCreate()
}

object Test {
  def main(args: Array[String]): Unit = {
    val name = args(0)
    val sessionTrait = new SparkSessionTrait(name)
    import sessionTrait._

    sparkSession.catalog.clearCache()
}