Polymorphic instantiation in Scala using TypeTag and ClassTag

Question

In Scala 2.9 one could implement polymorphic instantiation as

def newInstance[T](implicit m: Manifest[T]) =
    m.erasure.newInstance.asInstanceOf[T]
         


        

Answer 1

If you want to support passing args, here's a trick I do with 2.11:

def newInstance[T : ClassTag](init_args: AnyRef*): T = {
classTag[T].runtimeClass.getConstructors.head.newInstance(init_args: _*).asInstanceOf[T]
}

Example usage:

scala> case class A(x:Double, y:Int)
defined class A
scala> newInstance[A](4.5.asInstanceOf[Object],3.asInstanceOf[Object])
res1: A = A(4.5,3)