How do I get a generic runtime class in Scala?
import scala.reflect.runtime.universe._
import scala.reflect.ClassTag
import scala.reflect.classTag
def getTypeTag[T: TypeTag](obj: T) = println(typeTag[T].tpe)
class Entity
{
def greet = println("Hello!")
}
class Point[T : TypeTag](val x : T, val y :T) extends Entity
val p = new Point[Int](2,5)
val p2 = new Point[Float](1.0f,-5.0f)
val p3 = new Point[Double](4.0,-7.0)
val path = Array[Entity](p,p2,p3)
path.foreach(getTypeTag(_))
This small piece of code writes to stdout
Helper.this.Entity
Helper.this.Entity
Helper.this.Entity
I would like to write
Helper.this.Point[Int]
Helper.this.Point[Float]
Helper.this.Point[Double]
I know there are many questions about scala reflection, I have read a lot of them but still don't understand the difference between TypeTag, Manifest and ClassTag; and I cannot get this most basic example to work. Any help would be greatly appreciated.
Thank you in advance
+3
source to share
1 answer
Short, sane answer:
You can not. Do not do this. Why do you need this? You are probably wrong ...
Unsatisfactory answer:
def printType(a: Any) =
a match {
case p: Point[_] =>
val clazz = p.getClass.getName
val tname = p.x.getClass.getName
println(s"$clazz[$tname]")
case _ =>
println("yolo")
}
class Entity
class Point[T](val x: T, val y: T) extends Entity
val p = new Point[Int](2,5)
val p2 = new Point[Float](1.0f,-5.0f)
val p3 = new Point[Double](4.0,-7.0)
val path = Array[Entity](p, p2, p3)
path.foreach(printType)
Actual answer:
Use Shapeless Typeable .
import shapeless._
val path = p :: p2 :: p3 :: HNil
object printType extends Poly1 {
implicit def case0[T](implicit t: Typeable[T]) =
at[T](_ => t.describe)
}
path.map(printType).toList.foreach(println)
+1
source to share