Having trouble with curried parameter

Question

the code below runs perfectly fine if I simply make it a "case class". However, I certainly do not want that for a mutable object - but by changing it to a regular class, it no longer seems to understand the anonymous function parameter at the end. Not sure why I can't get past this, i've tried a few variations and can't understand why making it a case class works. (scala 2.10.2) - thanks

/**
 *
 * @param target  - can be any large target number
 * @param perPiece  - at what percentage interval is todo called
 * @param todo    - passed current percentage complete
 */
class ProgressTool(target:Double, perPiece:Double) (todo: (Double)=>Unit) extends Mutable {

  private[this] var lastUpdate:Double =0.0

  def update(atPos:Double) = {
    val step = atPos - lastUpdate

    if (step/target >=perPiece) {
      lastUpdate += step
      todo(lastUpdate)

    }
  }

}


object TestProgressTool extends App {

  val x = new ProgressTool(1000,.01) { x:Double =>
    println("Hello "+ x)
  }
}

missing arguments for constructor ProgressTool in class ProgressTool val x = new ProgressTool(1000,.01) { x:Double => ^

Answer 1

Using round parens around the second param list heals the code too and might be less surprising:

object TestProgressTool extends App {
  val x = new ProgressTool(1000,.01) ({ x:Double =>
    println("Hello "+ x)
  })
}

Answer 2

Not sure why it seems to work, but try this (note extra parentheses around constructor with first arguments):

object TestProgressTool extends App {

  val x = (new ProgressTool(1000,.01)) { x:Double =>
    println("Hello "+ x)
  }
}