Question

In ‘Programming in Scala, Second Edition’ at page 410 you can find class Simulation which have the following method:

private def next() {
  (agenda: @unchecked) match {
    case item :: rest =>
      agenda = rest
      curtime = item.time
      item.action()
  }
}

I’m curious why Odersky implemented this with pattern matching rather than just like that:

private def next() {
  val item = agenda.head
  agenda = agenda.tail
  curtime = item.time
  item.action()
}

Is pattern matching so efficient that it doesn’t matter at all?
Or it was just not so perfect example?

Answer 1

Normally I’d write it the way you did. (Even though pattern matching is quite efficient, it is not as efficient as head/tail.) You’d use pattern matching if

1. You wanted to practice pattern matching
2. You wanted a MatchException instead of a NoSuchElementException
3. You were going to fill in other cases later.