Scala3GivenMetric.scala

sealed trait Metric(val name: String, val description: String)

case class Counter(override val name: String,
                   override val description: String,
                   value: Double
                  ) extends Metric(name, description)

trait ToText[T <: Metric]:
  def toText(t: T): String

object ToTexts:
  given ToText[Counter] with
    def toText(t: Counter) =
      s"""|# HELP ${t.name} ${t.description}.
          |# TYPE ${t.name} counter
          |${t.name} ${t.value}
          |""".stripMargin


import ToTexts.given_ToText_Counter

def toText[A <: Metric](a: A)(using s: ToText[A]): String = summon[ToText[A]].toText(a)

@main
def main(): Unit = time {
  val c = Counter("cpu_total_seconds", "CPU total seconds", 60 * 20)
  println(toText(c))
}