Record Execution Time with WriterT

timed.scala

// From https://www.softwaretalks.io/v/4720/lambda-world-2018-boring-use-cases-for-exciting-types-itamar-ravid
  type Timed[A] = WriterT[Id, Map[String, FiniteDuration], A]

  def timed[A](name: String, lazyA: () => A): Timed[A] =
    WriterT[Id, Map[String, FiniteDuration], A] {
      timed(lazyA).leftMap(duration => Map(name -> duration))
    }

  trait TimedOps {
    def logMetric(): Unit
  }

  trait ToTimedOps {
    implicit def toTimedOps[A](target: Timed[A])(implicit logger: Logger): TimedOps =
      new TimedOps {
        override def logMetric(): Unit = {
          val (records, _) = target.run
          records.foreach { case (name, d) => logger.info(s"Execution time of $name $d")}
        }
      }
  }