Scala Cookbook

3.7. Using a Match Expression Like a switch Statement

Problem

You have a situation where you want to create something like a simple Java integer-based switch statement, such as matching the days in a week, months in a year, and other situations where an integer maps to a result.

Solution

To use a Scala match expression like a Java switch statement, use this approach:

// i is an integer
i match {
  case 1  => println("January")
  case 2  => println("February")
  case 3  => println("March")
  case 4  => println("April")
  case 5  => println("May")
  case 6  => println("June")
  case 7  => println("July")
  case 8  => println("August")
  case 9  => println("September")
  case 10 => println("October")
  case 11 => println("November")
  case 12 => println("December")
  // catch the default with a variable so you can print it
  case whoa  => println("Unexpected case: " + whoa.toString)
}

That example shows how to take an action based on a match. A more functional approach returns a value from a match expression:

val month = i match {
  case 1  => "January"
  case 2  => "February"
  case 3  => "March"
  case 4  => "April"
  case 5  => "May"
  case 6  => "June"
  case 7  => "July"
  case 8  => "August"
  case 9  => "September"
  case 10 => "October"
  case 11 => "November"
  case 12 => "December"
  case _  => "Invalid month"  // the default, catch-all
}

The @switch annotation

When writing simple match expressions like this, it’s recommend to use the @switch annotation. This annotation provides a warning at compile time if the switch can’t be compiled to a tableswitch ...