CODEWITHSUNDEEP
scalapattern-matchingswitch-statement
Ivan
Ivan

Reputation: 64227

How to use switch/case (simple pattern matching) in Scala?

I've found myself stuck on a very trivial thing :-]

I've got an enum:

 object Eny extends Enumeration {
      type Eny = Value
      val FOO, BAR, WOOZLE, DOOZLE = Value
    }

In a code I have to convert it conditionally to a number (varianr-number correspondence differs on context). I write:

val en = BAR
val num = en match {
  case FOO => 4
  case BAR => 5
  case WOOZLE => 6
  case DOOZLE => 7
}

And this gives me an "unreachable code" compiler error for every branch but whatever is the first ("case FOO => 4" in this case). What am I doing wrong?

Upvotes: 50

Views: 78214

Answers (2)

Daniel C. Sobral
Daniel C. Sobral

Reputation: 297265

I suspect the code you are actually using is not FOO, but foo, lowercase, which will cause Scala to just assign the value to foo, instead of comparing the value to it.

In other words:

x match {
  case A => // compare x to A, because of the uppercase
  case b => // assign x to b
  case `b` => // compare x to b, because of the backtick
}

Upvotes: 65

Matthew Farwell
Matthew Farwell

Reputation: 61705

The following code works fine for me: it produces 6

object Eny extends Enumeration {
  type Eny = Value
  val FOO, BAR, WOOZLE, DOOZLE = Value
}

import Eny._

class EnumTest {
    def doit(en: Eny) = {
        val num = en match {
          case FOO => 4
          case BAR => 5
          case WOOZLE => 6
          case DOOZLE => 7
        }       

        num
    }
}

object EnumTest {
    def main(args: Array[String]) = {
        println("" + new EnumTest().doit(WOOZLE))
    }
}

Could you say how this differs from your problem please?

Upvotes: 7

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