I want to use scala macros to do some kind of code generation. In specific, I define some Event
types and these events will be pushed to the same method (here workImpl
) and return a value of a specific type. The return type is not determined if I just call workImpl
, because it handles different inputs and returns different results. But the map between input types and output types is determined . The goal is to make the return type available.
Scala macro is fantastic and maybe helps. I want to achieve auto code generation by add event return type annotation for each event type. The code that is supposed to be generated is code1
or code2
.
object A {
private def workImpl(x: Any): Any = ???
@anno(X_RET)
case class X()
@anno(Y_RET)
case class Y()
@anno(Z_RET)
case class Z()
// code1: auto generate work1 and the implicits
def work1[T](x:T)(implicit ev: T=>M) = workImpl(x).asInstanceOf[M]
implicit val X_TO_X_RET: X=>X_RET = null
implicit val Y_TO_Y_RET: Y=>Y_RET = null
implicit val Z_TO_Z_RET: Z=>Z_RET = null
// code2: auto generate these methods
def work2(x:X) = workImpl(x).asInstanceOf[X_RET]
def work2(x:Y) = workImpl(x).asInstanceOf[Y_RET]
def work2(x:Z) = workImpl(x).asInstanceOf[Z_RET]
}
So, is this possible and how to achieve this? If it is not possible, any solution else?
I finally find a solution that works.
object A {
private def workImpl(x: Any): Any = x match {
case e: X => XRet(0)
case e: Y => YRet(0)
case e: Z => ZRet(0)
}
trait Event
trait EventReturn[T] extends Event
case class X() extends EventReturn[XRet]
case class Y() extends EventReturn[YRet]
case class Z() extends EventReturn[ZRet]
case class XRet(x:Int)
case class YRet(y:Int)
case class ZRet(z:Int)
def work3[T](x: EventReturn[T]): T = workImpl(x).asInstanceOf[T]
def main(args: Array[String]): Unit = {
work3(X()).x
work3(Y()).y
work3(Z()).z
}
}
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