How do you pattern match an empty Map? - scala

Question

I've got a Map and I'd like to have different behavior if it's empty or not. I cannot figure out how to match an empty map. I've consulted other answers and pattern matching documentation, and I can't figure it out. I thought that Nil might work like it does for lists, but that isn't the case. I also can't seem to match against Map(), Map[String, String].empty or Map[String, String]()
myMap match {
// doesn't work
case Nil => false
case _ => true
}
myMap match {
// also doesn't work
case Map[String, String]() => false
case _ => true
}
The approaches in this answer seem like overkill for checking if a Map is empty. Also, the accepted answer checks if the Map contains any of the maps to be matched, which I do not think would apply in my situation

Answer 1

Map doesn't provide any extractor with unapply()/unapplySeq() methods out of the box, so it is impossible to match key-value pairs it in pattern matching. But if you need only to match if map is empty you can:
val map = Map.empty[String, String]
val result = map match {
case m:Map[String, String] if m.isEmpty => false
case _ => true
}
println(result)
outputs:
false

Answer 2

Map doesn't have an unapply()/unapplySeq() method so it can't deconstructed via pattern matching.
As #Luis has commented, Nil is the List terminus and unrelated to Map.

Answer 3

Without over using patten mathing:
val map = Map.empty[String, String]
val result = map.nonEmpty
println(result)
// Output: false
Or if you insist or have more logic than just true/false:
val map = Map.empty[String, String]
map.isEmpty match {
case true =>
println("The map is empty")
case false =>
println("The map is not empty")
}
// Output: The map is empty