Can a range be matched in Scala?

Question

Is it possible to match a range of values in Scala?

For example:

val t = 5
val m = t match {
    0 until 10 => true
    _ => false
}

m would be true if t was between 0 and 10, but false otherwise. This little bit doesn't work of course, but is there any way to achieve something like it?

Note that by writing "0 until 10" you mean 0, 1, 2, ..., 9 (including 0, excluding 10). If you want to include 10, use "0 to 10". — Jesper, Aug 28 '09 at 11:11
See a related stackoverflow question: [How can I pattern match on a range in Scala?](http://stackoverflow.com/questions/3160888/how-can-i-pattern-match-on-a-range-in-scala) — David J., Sep 26 '11 at 01:35
The title asks for how to match a value of type `Range` against several possibilities, e.g. "Do I have `(0..5)` or `(1..6)`?" — Raphael, Sep 26 '11 at 18:33
`val m = 0 until 10 contains t` is effectively the same but shorter. it will get you the true/false answer. If a boolean answer is all you are after. — Peter Perháč, May 14 '17 at 18:59

score 81 · Accepted Answer · answered Aug 28 '09 at 10:48

81

Guard using Range:

val m = t match {
  case x if 0 until 10 contains x => true
  case _ => false
}

answered Aug 28 '09 at 10:48

Alexander Azarov

12,971
2
50
54

1

what about Double? 0.1 and 10.0 – Oleg Abrazhaev Jun 19 '18 at 09:11
@OlegAbrazhaev what's about it? – Alexander Azarov Jun 19 '18 at 18:50
@AlexanderAzarov how to implement it? Could you add an example for doubles? The step will be 0.1, not 1. – Oleg Abrazhaev Jun 20 '18 at 09:14
1

@OlegAbrazhaev in REPL: `scala> 0.0 until 10.0 by 0.1 contains 4.0`, returns `res0: Boolean = true` – Alexander Azarov Jun 20 '18 at 11:02

score 34 · Answer 2 · answered Aug 28 '09 at 10:43

34

You can use guards:

val m = t match {
    case x if (0 <= x && x < 10) => true
    case _ => false
}

answered Aug 28 '09 at 10:43

Alexey Romanov

167,066
35
309
487

3

In terms of performance this solution is better than @alexander-azarov solution. There the Range needs to be initialised followed by a range scan. Especially for large ranges this can become a problem. – Oosterman May 20 '16 at 06:54
1

`Range.contains` is of course overridden so it doesn't need to scan anything! It's still a bit of extra code, but Hotspot should inline and optimize it without problem. – Alexey Romanov May 20 '16 at 08:33

score 4 · Answer 3 · answered Sep 26 '14 at 12:47

With these definitions:

  trait Inspector[-C, -T] {
    def contains(collection: C, value: T): Boolean
  }

  implicit def seqInspector[T, C <: SeqLike[Any, _]] = new Inspector[C, T]{
    override def contains(collection: C, value: T): Boolean = collection.contains(value)
  }

  implicit def setInspector[T, C <: Set[T]] = new Inspector[C, T] {
    override def contains(collection: C, value: T): Boolean = collection.contains(value)
  }

  implicit class MemberOps[T](t: T) {
    def in[C](coll: C)(implicit inspector: Inspector[C, T]) =
      inspector.contains(coll, t)
  }

You can do checks like these:

2 in List(1, 2, 4)      // true
2 in List("foo", 2)     // true
2 in Set("foo", 2)      // true
2 in Set(1, 3)          // false
2 in Set("foo", "foo")  // does not compile
2 in List("foo", "foo") // false (contains on a list is not the same as contains on a set)
2 in (0 to 10)          // true

So the code you need would be:

val m = x in (0 to 10)

score 3 · Answer 4 · answered Jul 02 '12 at 04:28

3

Here's another way to match using a range:

val m = t match {
  case x if ((0 to 10).contains(x)) => true
  case _ => false
}

answered Jul 02 '12 at 04:28

swartzrock

729
5
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1

This duplicates @Alexander Azarov's answer. – Glenn Feb 12 '15 at 15:14
Wrong match for t == 10. – Alexander Prokofyev Sep 23 '16 at 16:58

score 2 · Answer 5 · answered Apr 01 '18 at 13:20

Another option would be to actually add this to the language using implicits, i added two variations for int and Range

object ComparisonExt {
  implicit class IntComparisonOps(private val x : Int) extends AnyVal {
    def between(range: Range) = x >= range.head && x < range.last
    def between(from: Int, to: Int) = x >= from && x < to
  }

}

object CallSite {
  import ComparisonExt._

  val t = 5
  if (t between(0 until 10)) println("matched")
  if (!(20 between(0 until 10))) println("not matched")
  if (t between(0, 10)) println("matched")
  if (!(20 between(0, 10))) println("not matched")
}

Can a range be matched in Scala?

5 Answers5

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