Scala Language Pattern Matching Guards (if expressions)
Example
Case statements can be combined with if expressions to provide extra logic when pattern matching.
def checkSign(x: Int): String = {
x match {
case a if a < 0 => s"$a is a negative number"
case b if b > 0 => s"$b is a positive number"
case c => s"$c neither positive nor negative"
}
}
It is important to ensure your guards do not create a non-exhaustive match (the compiler often will not catch this):
def f(x: Option[Int]) = x match {
case Some(i) if i % 2 == 0 => doSomething(i)
case None => doSomethingIfNone
}
This throws a MatchError on odd numbers. You must either account for all cases, or use a wildcard match case:
def f(x: Option[Int]) = x match {
case Some(i) if i % 2 == 0 => doSomething(i)
case _ => doSomethingIfNoneOrOdd
}
