Scala: "recursive value ... needs type" but I use Java types only

Question

object Rec extends App {
  val outStream = new java.io.ByteArrayOutputStream
  {
    val out = new java.io.PrintStream(new java.io.BufferedOutputStream(outStream))
  }
}

This seemingly simple code causes a compile error:

$ scalac rec.scala
rec.scala:2: error: recursive value out needs type
  val outStream = new java.io.ByteArrayOutputStream
                  ^
one error found

But I don't see what is "recursive."

Background: I was trying to write a unit test on println with Console.withOut

score 4 · Answer 1 · answered Jan 26 '16 at 12:15

You are assigning a value to outStream by invoking stuff to which you pass on the outStream (I marked it in CAPS). Hence the recursion.

object Rec extends App {
  val OUTSTREAM = new java.io.ByteArrayOutputStream
  {
    val out = new java.io.PrintStream(new java.io.BufferedOutputStream(OUTSTREAM))
  }
}

score 4 · Accepted Answer · edited May 23 '17 at 11:45

After putting braces where they belong code looks like this:

object Rec extends App {
  val outStream = new java.io.ByteArrayOutputStream {
    val out = new java.io.PrintStream(new java.io.BufferedOutputStream(outStream))
  }
}

and this is how you create object of an anonymous class with a member out that uses the defined object recursively (outStream uses outStream in its definition).

I believe this is what you wanted to do

object Rec extends App {
  val outStream = new java.io.ByteArrayOutputStream
  val out = new java.io.PrintStream(new java.io.BufferedOutputStream(outStream))
}

If you for some reason need to create another scope, you can use locally

What does Predef.locally do, and how is it different from Predef.identity

Thanks for telling me about `locally` – nodakai Jan 28 '16 at 07:56 — nodakai, Jan 28 '16 at 07:56

Scala: "recursive value ... needs type" but I use Java types only

2 Answers2

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