Why does the Scala Macro for case class copy fail? - scala

Question

I have about 24 Case classes that I need to programatically enhance by changing several common elements prior to serialization in a datastore that doesn't support joins. Since case classes don't have a trait defined for the copy(...) constructor, I have been attempting to use Macros - As a base I've looked at
this post documenting a macro and come up with this macro:
When I try to compile, I get the following:
import java.util.UUID
import org.joda.time.DateTime
import scala.language.experimental.macros
trait RecordIdentification {
val receiverId: Option[String]
val transmitterId: Option[String]
val patientId: Option[UUID]
val streamType: Option[String]
val sequenceNumber: Option[Long]
val postId: Option[UUID]
val postedDateTime: Option[DateTime]
}
object WithRecordIdentification {
import scala.reflect.macros.Context
def withId[T, I](entity: T, id: I): T = macro withIdImpl[T, I]
def withIdImpl[T: c.WeakTypeTag, I: c.WeakTypeTag](c: Context)(
entity: c.Expr[T], id: c.Expr[I]
): c.Expr[T] = {
import c.universe._
val tree = reify(entity.splice).tree
val copy = entity.actualType.member(newTermName("copy"))
val params = copy match {
case s: MethodSymbol if (s.paramss.nonEmpty) => s.paramss.head
case _ => c.abort(c.enclosingPosition, "No eligible copy method!")
}
c.Expr[T](Apply(
Select(tree, copy),
AssignOrNamedArg(Ident("postId"), reify(id.splice).tree) ::
AssignOrNamedArg(Ident("patientId"), reify(id.splice).tree) ::
AssignOrNamedArg(Ident("receiverId"), reify(id.splice).tree) ::
AssignOrNamedArg(Ident("transmitterId"), reify(id.splice).tree) ::
AssignOrNamedArg(Ident("sequenceNumber"), reify(id.splice).tree) :: Nil
))
}
}
And I invoke it with something like:
class GenericAnonymizer[A <: RecordIdentification]() extends Schema {
def anonymize(dataPost: A, header: DaoDataPostHeader): A = WithRecordIdentification.withId(dataPost, header)
}
But I get a compile error:
Error:(44, 71) type mismatch;
found : com.dexcom.rt.model.DaoDataPostHeader
required: Option[String]
val copied = WithRecordIdentification.withId(sampleGlucoseRecord, header)
Error:(44, 71) type mismatch;
found : com.dexcom.rt.model.DaoDataPostHeader
required: Option[java.util.UUID]
val copied = WithRecordIdentification.withId(sampleGlucoseRecord, header)
Error:(44, 71) type mismatch;
found : com.dexcom.rt.model.DaoDataPostHeader
required: Option[Long]
val copied = WithRecordIdentification.withId(sampleGlucoseRecord, header)
I'm not quite sure how to change the macro to support multiple parameters... any sage advice?

Answer 1

Assuming you have a set of following case classes, which you wish to anonymize on certain attributes prior to serialization.
case class MyRecordA(var receiverId: String, var y: Int)
case class MyRecordB(var transmitterId: Int, var y: Int)
case class MyRecordC(var patientId: UUID, var y: Int)
case class MyRecordD(var streamType: String, var y: Int)
case class MyRecordE(var sequenceNumber: String, var streamType: String, var y: Int)
You can use scala reflection library to mutate an instance's attributes in runtime. You can implement your custom anonymize/enhancing logic in implicit anonymize method that the Mutator can use to alter a given instance's field selectively if required as per your implementation.
import java.util.UUID
import scala.reflect.runtime.{universe => ru}
implicit def anonymize(field: String /* field name */, value: Any /* use current field value if reqd */): Option[Any] = field match {
case "receiverId" => Option(value.toString.hashCode)
case "transmitterId" => Option(22)
case "patientId" => Option(UUID.randomUUID())
case _ => None
}
implicit class Mutator[T: ru.TypeTag](i: T)(implicit c: scala.reflect.ClassTag[T], anonymize: (String, Any) => Option[Any]) {
def mask = {
val m = ru.runtimeMirror(i.getClass.getClassLoader)
ru.typeOf[T].members.filter(!_.isMethod).foreach(s => {
val fVal = m.reflect(i).reflectField(s.asTerm)
anonymize(s.name.decoded.trim, fVal.get).foreach(fVal.set)
})
i
}
}
Now you can invoke masking on any instance as:
val maskedRecord = MyRecordC(UUID.randomUUID(), 2).mask