Pattern Matching in Scala
December 29, 2014
2 min read
Pattern matching is one of many things that Scala can do.
Think „switch” on steroids. What happens if you have to match one or more patterns in a match expression, and the pattern may be a constant, variable, constructor, sequence, tuple, or type pattern. In Scala this is kid's play.
The following example explains how this could be made in Scala.
def echoWhateverYouGaveMe(x: Any): String = x match {
// constant patterns
case 0 => "zero"
case true => "true"
case "hello" => "you said 'hello'"
case Nil => "an empty List"
// sequence patterns
case List(0, _, _) => "a three-element list with 0 as the first element"
case List(1, _*) => "a list beginning with 1, having any number of elements"
case Vector(1, _*) => "a vector starting with 1, having any number of elements"
// tuples
case (a, b) => s"got $a and $b"
case (a, b, c) => s"got $a, $b, and $c"
// constructor patterns
case Person(first, "Alexander") => s"found an Alexander, first name = $first"
case Dog("Suka") => "found a dog named Suka"
// typed patterns
case s: String => s"you gave me this string: $s"
case i: Int => s"thanks for the int: $i"
case f: Float => s"thanks for the float: $f"
case a: Array[Int] => s"an array of int: ${a.mkString(",")}"
case as: Array[String] => s"an array of strings: ${as.mkString(",")}"
case d: Dog => s"dog: ${d.name}"
case list: List[_] => s"thanks for the List: $list"
case m: Map[_, _] => m.toString
// the default wildcard pattern
case _ => "Unknown"
// adding if expressions
case a if 0 to 9 contains a => println("0-9 range: " + a)
case b if 10 to 19 contains b => println("10-19 range: " + b)
case x if x == 1 => println("one, a lonely number")
case x if (x == 2 || x == 3) => println(x)
case _ => println("some other value")
// matching multiple conditions with one case statement
case 1 | 3 | 5 | 7 | 9 => println("odd")
case 2 | 4 | 6 | 8 | 10 => println("even")
}
