Frame.scala

import scala.compiletime._
import scala.compiletime.ops.any

final case class Col[Key, Value](data: Array[Value]) 

object Frame {
  object Types {
    type Get[F <: Tuple, Key] = 
      F match {
        case Col[Key, v] *: cols => v
        case Col[k, v] *: cols => Get[cols, Key]
        case _ => Nothing
      }
  }

  inline def get[Key, F <: Tuple](frame: F): Array[Types.Get[F, Key]] =
    inline frame match {
      case () => error("The frame did not have an element with the given key.")
      case (c: Col[k, v]) *: cols => 
        inline if(constValue[any.==[Key, k]]) c.data.asInstanceOf[Array[Types.Get[F, Key]]] else get[Key, cols.type](cols).asInstanceOf[Array[Types.Get[F, Key]]]
      case _ => error("This is not a valid frame. It does not contain a tuple of Col.")
    }

  val frame: Col["firstName", String] *: Unit = (Col["firstName", String](Array("Dotty")) *: ())
  get[Key="firstName"](frame)
  // Fails with
  // error] -- Error: Frame.scala:25:22 -----
  // [error] 25 |  get[Key="firstName"](frame)
  // [error]    |  ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  // [error]    |  This is not a valid frame. It does not contain a tuple of Col.
  //
  // Remove the catch all pattern from get and the compilation fails with
  // [error] -- Error: Frame.scala:25:22 -----
  // [error] 25 |  get[Key="firstName"](frame)
  // [error]    |  ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  // [error]    |cannot reduce inline match with
  // [error]    | scrutinee:  {
  // [error]    |  Frame.frame
  // [error]    |} : (Frame.frame : Col[("firstName" : String), String] *: Unit)
  // [error]    | patterns :  case ()
  // [error]    |             case *:.unapply[Any, Tuple](c @ _:Col[k @ _, v @ _], cols @ _):Any *: Tuple
  // [error]    | This location contains code that was inlined from Frame.scala:17
}