CODEWITHSUNDEEP
scalascala-3
gekomad
gekomad

Reputation: 565

Scala 3 - generic programming with Product

According to https://www.scala-lang.org/2021/02/26/tuples-bring-generic-programming-to-scala-3.html

I can write correctly:

def tupleToCsv[A <: Tuple : RowEncoder](tuple: A): List[String] = summon[RowEncoder[A]].encodeRow(tuple)

case class Employee(name: String, number: Int, manager: Boolean)

val t = Tuple.fromProductTyped(Employee("Bob", 42, false))
println(tupleToCsv(t)) // List(Bob, 42, false)

but I'd like write a unique method toCsv

   def toCsv[A <: Product](t: A)(using m: scala.deriving.Mirror.ProductOf[A]):  List[String] = {
      val tuple = Tuple.fromProductTyped(t)
      val aa = summon[RowEncoder[A]] // ***
      aa.encodeRow(tuple)
    }

and call it with toCsv(Employee("Bob", 42, false))

the compiler at row *** says:

no implicit argument of type RowEncoder[A] was found for parameter x of method summon in object Predef
where:    A is a type in method toCsv with bounds <: Product
      val aa = summon[RowEncoder[A]]

how can I provide automatic derivation for A ?

Upvotes: 4

Views: 310

Answers (1)

esse
esse

Reputation: 1551

Here it is:

def toCsv[A <: Product](t: A)(using m: scala.deriving.Mirror.ProductOf[A], e: RowEncoder[m.MirroredElemTypes]): List[String] =
    e.encodeRow(Tuple.fromProductTyped(t))

Upvotes: 2

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