Question

When I “sbt run” the following code,

package com.example

import java.io.ObjectInputStream
import java.io.ObjectOutputStream
import java.io.FileInputStream
import java.io.FileOutputStream

object SimpleFailure extends App {
  case class MyClass(a: String, b: Int, c: Double)

  def WriteObjectToFile[A](obj: A, filename: String) {
    val output = new ObjectOutputStream(new FileOutputStream(filename, false))
    output.writeObject(obj)
  }  

  def ReadObjectFromFile[A](filename: String)(implicit m: Manifest[A]): A = {
    val obj = new ObjectInputStream(new FileInputStream(filename)) readObject

    obj match {
      case a if m.erasure.isInstance(a) => a.asInstanceOf[A]
      case _ => { sys.error("Type not what was expected when reading from file") }
    }
  }

  val orig = MyClass("asdf", 42, 2.71)
  val filename = "%s/delete_me.spckl".format(System.getProperty("user.home"))

  WriteObjectToFile(List(orig), filename)

  val loaded = try {
    ReadObjectFromFile[List[MyClass]](filename)
  } catch { case e => e.printStackTrace; throw e }

  println(loaded(0))
}

I get the following exception:

java.lang.ClassNotFoundException: com.example.SimpleFailure$MyClass

However, I can run the code fine in Eclipse with the Scala plugin. Is this an SBT bug? Interestingly, the problem only comes up when wrapping MyClass in a List (see how “orig” is wrapped in a List in the WriteObjectToFile call). If I don’t wrap in a List, everything works fine.

Answer 1

I was able to reproduce this too using sbt 0.10.1 and scalaVersion := "2.9.0-1". You should probably just report it on github or bring it up on the mailing list.