Scala3 TypeClass example with using/given

output.txt

6
123
Some(456)

Scala3TypeClassWithUsingGiven

object Scala3TypeClassWithUsingGiven {

  trait MyMonoid[A] {
    def combine(x: A, y: A): A
    def empty: A
  }

  def combineList[A](li: List[A])(using monoid: MyMonoid[A]): A = li.foldLeft(monoid.empty)(monoid.combine)

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

    given addInts: MyMonoid[Int] with {
      override def combine(x: Int, y: Int): Int = x + y

      override def empty: Int = 0
    }

    val sum = combineList(List(1, 2, 3))

    println(sum)

    given addStrings: MyMonoid[String] with {
      override def combine(x: String, y: String): String = x + y

      override def empty: String = ""
    }

    val bigString = combineList(List("1", "2", "3"))

    println(bigString)

    // composing new Option[instance] from existing instance
    given optionMonoid[T](using monoid: MyMonoid[T]) : MyMonoid[Option[T]] with {
      override def combine(xo: Option[T], yo: Option[T]): Option[T] = for {
        x<- xo
        y <- yo
      } yield monoid.combine(x,y)

      override def empty: Option[T] = Some(monoid.empty)
    }

    val bigOptionString = combineList(List(
      Option("4"),
      Option("5"),
      Option("6")
    ))

    println(bigOptionString)

  }

}