scala - How to supply transformed params to superclass constructor while avoiding inline computations with Scala

Question

This is my current unsatisfactory solution to the problem of manipulating the values passed to the subclass constructor before passing onto the superclass constructor,

class MissingItemsException(items: Set[String], itemsCategory: String)
  extends RuntimeException(MissingItemsException.makeMessage(items, itemsCategory))

private object MissingItemsException {

  private def makeMessage(items: Set[String], itemsCategory: String): String = {
    /* Format set as ['α','β','γ'] */
    val Items = items mkString ("['", "','", "']")
    "the following items %s were missing from '%s'" format (items, itemsCategory)
  }

}

Is there a way of factoring out the transformation so that the transformation code remains close to the point of use while keeping the code legible?

Answer 1

您可以使用早期初始化程序：

class MissingItemsException(items: Set[String], itemsCategory: String) extends {
  val customMessage = {
    val Items = items mkString ("['", "','", "']")
    "the following items %s were missing from '%s'" format (items, itemsCategory)
  }
} with RuntimeException( customMessage );

从老式的词法作用域的角度来看，它甚至可以编译是很奇怪的。但是编译它会做，它会做你想做的事！不过，它是否比您的解决方案“更好”是一个品味问题。