Turning inlined varargs into a generic tuple

[soronpo]

I've tried to do this, but I'm hitting a wall. How can I convert varargs to a tuple generically, without loosing the type narrowness.
E.g.:

transparent inline def toTuple(inline args : Int*) : Tuple 

val x : (1, 2, 3) = toTuple(1,2,3)

[nicolasstucki]

import scala.quoted.*

def toTupleExpr(argsExpr: Expr[Seq[Int]])(using Quotes): Expr[Tuple] = {
  argsExpr match
    case Varargs(argExprs) =>
      argExprs.foldRight[Expr[Tuple]]('{EmptyTuple}) { (expr, acc) =>
        (expr, acc) match // match to extract precise type
          case ('{ $expr: head }, '{ type tail <: Tuple; $acc: `tail` }) =>
            '{ $expr *: $acc }
      }
    case _ =>
      quotes.reflect.report.throwError(
        "Expected explicit argument list but got: " + argsExpr.show, argsExpr)
}

transparent inline def toTuple(inline args : Int*) : Tuple =
 ${ toTupleExpr('args) }

val x : (1, 2, 3) = toTuple(1,2,3)

[nicolasstucki]

I noticed that some of the tuple optimizations to convert 1 *: 2 *: 3 *: EmptyTuple into Tuple3(1, 2, 3) are not kicking in.

[soronpo]

I noticed that some of the tuple optimizations to convert 1 *: 2 *: 3 *: EmptyTuple into Tuple3(1, 2, 3) are not kicking in.

Scala is an eager widener 😉

Do you think this method has a place in the official compiler library as a varargs apply method under the Tuple object?

[nicolasstucki]

I would first create a library with it and see how many use cases there are.