Pattern matching against Scala Map type

Question

Imagine I have a Map[String, String] in Scala.

I want to match against the full set of key–value pairings in the map.

Something like this ought

Answer 1

You could just look up the values in question, stick them in a tuple, and pattern match on that:

val record = Map("amenity" -> "restaurant", "cuisine" -> "chinese", "name" -> "Golden Palace")
(record.get("amenity"), record.get("cuisine")) match {
    case (Some("restaurant"), Some("chinese")) => "a Chinese restaurant"
    case (Some("restaurant"), Some("italian")) => "an Italian restaurant"
    case (Some("restaurant"), _) => "some other restaurant"
    case _ => "something else entirely"
}

Or, you could do some nested matches, which might be a bit cleaner:

val record = Map("amenity" -> "restaurant", "cuisine" -> "chinese", "name" -> "Golden Palace")
record.get("amenity") match {
  case Some("restaurant") => record.get("cuisine") match {
    case Some("chinese") => "a Chinese restaurant"
    case Some("italian") => "an Italian restaurant"
    case _ => "some other restaurant"
  }
  case _ => "something else entirely"
}

Note that map.get(key) returns an Option[ValueType] (in this case ValueType would be String), so it will return None rather than throwing an exception if the key doesn't exist in the map.