Scala: Copying a generic case class into another - scala

Question

I have the following setup, where I want to copy an instance of baseData into that of moreData:
sealed trait baseData {
def weight: Int
def priority: Int
}
sealed trait moreData {
def weight: Int
def priority: Int
def t: String
def id: String
}
case class data1(override val weight: Int, override val priority: Int) extends baseData
case class moreData1 (override val weight:Int, override val priority: Int, override val t: String, override val id: String)extends moreData
So copying myData into otherData below:
val myData = data1(1,1)
val otherData = moreData1 (2,2,"C","abcd")
would yield: moreData1(1,1,"C","abcd").
To do this, I want to use a function with the following signature, because I will have more than one case class extending both baseData and moreData:
def copyOver[A <:baseData, B <:moreData](from: A, to: B) = {}
I'm sure you can do this with Shapeless, but haven't figured out how. There are examples (here) on copying case classes extending a same trait, and others (here) mapping values between different case classes via generic representation. But I haven't figured out how to use LabelledGeneric with the trait-bounded arguments passed into copyOver. I also don't want to have to hardcode the extra fields in otherData that aren't present in myData.
I'm looking for a completely generic implementation. Any ideas?

Answer 1

You should be able to use the UpdateRepr type class from your first shapeless example.
You could define copyOver using UpdateRepr as follows :
import shapeless._
// baseData, moreData, data1, moreData1
// UpdateRepr ...
def copyOver[A <: baseData, B <: moreData, R <: HList](
from: A,
to: B
)(implicit
lgen: LabelledGeneric.Aux[A, R],
update: UpdateRepr[B, R]
): B = update(to, lgen.to(from))
Which you could use as follows :
val myData = data1(1,1)
val otherData = moreData1(2,2,"C","abcd")
copyOver(myData, otherData)
// moreData1 = moreData1(1,1,C,abcd)
Note that it is possible you run into problems with SI-7046, because of the sealed trait (Coproduct) type class derivation for UpdateRepr, which you could notice in the REPL or when splitting UpdateRepr and the sealed traits over multiple files.