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

Another version which requires you to specify the keys you want to extract and allows you to match on the values is the following:

class MapIncluding[K](ks: K*) {
  def unapplySeq[V](m: Map[K, V]): Option[Seq[V]] = if (ks.forall(m.contains)) Some(ks.map(m)) else None
}

val MapIncludingABC = new MapIncluding("a", "b", "c")
val MapIncludingAAndB = new MapIncluding("a", "b")

Map("a" -> 1, "b" -> 2) match {
  case MapIncludingABC(a, b, c) => println("Should not happen")
  case MapIncludingAAndB(1, b) => println(s"Value of b inside map is $b")
}