Scala: Use implicits in with Function interface

Question

In scala you can write a a function like:

object Add extends ((Int, Int) => Int) {
  def apply(a: Int, b: Int) = a + b
}

I want to write a function like above, but i also want to use imlicit. something like:

object DoSomething extends (Configuration, ??? => Dataframe) {
  override def apply(config: Configuration)(implicit sparkSession: SparkSession): DataFrame = {
    ...
  }
}

Does anyone know, how I can do this?

Edit:

object DoSomething extends (Configuration => SparkSession) {
  override def apply(config: Configuration)(implicit sparkSession: SparkSession): DataFrame = {
    val bootstrapServers = configuration.bootstrapServers
    val topic = configuration.topic

    sparkSession.readStream
      .format("kafka")
      .option("kafka.bootstrap.servers", bootstrapServers)
      .option("subscribe", topic)
      .load()
  }
}

Again it would be easier if you just have a plain object, and you define your apply there, which can receive an implicit. — Luis Miguel Mejía Suárez
– Luis Miguel Mejía Suárez, Commented Sep 9, 2019 at 12:12

Dmytro Mitin · Accepted Answer · 2019-09-09 12:03:30Z

1

Try

class DoSomething(implicit sparkSession: SparkSession) extends (Configuration => DataFrame) {
  override def apply(config: Configuration): DataFrame = {
    val bootstrapServers = configuration.bootstrapServers
    val topic = configuration.topic

    sparkSession.readStream
      .format("kafka")
      .option("kafka.bootstrap.servers", bootstrapServers)
      .option("subscribe", topic)
      .load()
  }
}

edited Sep 9, 2019 at 12:03

answered Sep 9, 2019 at 11:46

Dmytro Mitin

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5 Comments

SleepyX667 Over a year ago

Sorry that ??? I added because I didn't know how to mark the place where I thought the imlpicit definition should be or how it should look like.

Dmytro Mitin Over a year ago

@SleepyX667 Your apply returns DataFrame but there is no DataFrame in (Configuration, ??? => SparkSession).

SleepyX667 Over a year ago

I added a edit comment to the question and correct the typo I made (you are right... the function should return a Dataframe

Dmytro Mitin Over a year ago

@SleepyX667 Maybe this should be object DoSomething extends (Configuration => DataFrame). If method is def apply(x: X): Y then class extends (X => Y).

Dmytro Mitin Over a year ago

@SleepyX667 You can't put implicit to function type. This feature will appear only in Scala 3 dotty.epfl.ch/docs/reference/contextual/…

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