Question

I’d like to read a serialized object from a file in Scala, recovering functionality similar to Python’s pickle. My broken object reading code looks like this:

def ReadObjectFromFile[A](filename: String): A = {
  val input = new ObjectInputStream(new FileInputStream(filename))
  val obj = input.readObject()
  obj match {
    case a: A => a
    case _ => sys.error("Type not what was expected when reading from file")
  }
}

However, this code results in the warning “abstract type A in type pattern A is unchecked since it is eliminated by erasure”. What is the proper way to do this?

Answer 1

You can use implicits to get around type erasure as described in this blog post:

def ReadObjectFromFile[A](filename: String)(implicit m:scala.reflect.Manifest[A]): A = {
  val input = new ObjectInputStream(new FileInputStream(filename))
  val obj = input.readObject()
  obj match {
    case x if m.erasure.isInstance(x) => x.asInstanceOf[A]
    case _ => sys.error("Type not what was expected when reading from file")
  }
}