I have the following dummy Scala code in the file test.scala:

class Transaction {
  def begin() {}
  def commit() {}
  def rollback() {}
}

object Test extends Application {
  def doSomething() {}

  val t = new Transaction()
  t.begin()
  try {
    doSomething()
    t.commit()
  } catch {
    case _ => t.rollback()
  }
}

If I compile this on Scala 2.8 RC1 with scalac -Xstrict-warnings test.scala I'll get the following warning:

test.scala:16: warning: catch clause swallows everything: not advised.
    case _ => t.rollback()
    ^
one warning found

So, if catch-all expressions are not advised, how am I supposed to implement such a pattern instead? And apart from that why are such expressions not advised anyhow?