We need a generic way to make a copy of Product value from an example, but without knowing anything statically except that it's a Product. E.g., if we have
abstract class Exp
case class Add(l : Exp, r : Exp) extends Exp
case class Num(i : Int) extends Exp
then we might have Add(1,2) and want to make a copy of this node with new components 3 and 4, so we get an Add(3, 4) instance. If we knew statically that it was an Add (or even maybe Exp would be enough) we could use the copy method. But since we are doing this in a generic traversal, all we know is that it's of some type T <: Product, and copy is not generic.
Currently, we do this via reflection to get the constructor from the known value and call it with the new arguments. This works but ties us to reflection. It would be great to find a way to do this without needing reflection.
We need a generic way to make a copy of Product value from an example, but without knowing anything statically except that it's a Product. E.g., if we have
then we might have Add(1,2) and want to make a copy of this node with new components 3 and 4, so we get an Add(3, 4) instance. If we knew statically that it was an Add (or even maybe Exp would be enough) we could use the
copymethod. But since we are doing this in a generic traversal, all we know is that it's of some typeT <: Product, andcopyis not generic.Currently, we do this via reflection to get the constructor from the known value and call it with the new arguments. This works but ties us to reflection. It would be great to find a way to do this without needing reflection.