Is it possible to match on a comparison using the pattern matching system in Scala? For example:
a match {
case 10 => println("ten")
case _ > 10 => println("greater than ten")
case _ => println("less than ten")
}
The second case statement is illegal, but I would like to be able to specify "when a is greater than".
While all the above and bellow answers perfectly answer the original question, some additional information can be found in the documentation https://docs.scala-lang.org/tour/pattern-matching.html , they didn't fit in my case but because this stackoverflow answer is the first suggestion in Google I would like to post my answer which is a corner case of the question above.
My question is:
Which can be paraphrased:
The answer is the code example below:
def drop[A](l: List[A], n: Int): List[A] = l match {
case Nil => sys.error("drop on empty list")
case xs if n <= 0 => xs
case _ :: xs => drop(xs, n-1)
}
link to scala fiddle : https://scalafiddle.io/sf/G37THif/2
as you can see the case xs if n <= 0 => xs statement is able to use n(argument of a function) with the guard(if) statement.
I hope this helps someone like me.
Scala's pattern matching allows you to define your own extractor. In this case, you can simply define a new extractor:
class GreaterThan(n: Int) {
def unapply(i: Int) = i > n
}
val GreaterThan10 = GreaterThan(10)
a match {
case 10 => ???
case GreaterThan10() => ???
case _ => ???
}
or just use pattern guards.