Scala Cookbook

3.10. Accessing the Value of the Default Case in a Match Expression

Problem

You want to access the value of the default, “catch all” case when using a match expression, but you can’t access the value when you match it with the _ wildcard syntax.

Solution

Instead of using the _ wildcard character, assign a variable name to the default case:

i match {
  case 0 => println("1")
  case 1 => println("2")
  case default => println("You gave me: " + default)
}

By giving the default match a variable name, you can access the variable on the right side of the statement.

Discussion

The key to this recipe is in using a variable name for the default match instead of the usual _ wildcard character.

The name you assign can be any legal variable name, so instead of naming it default, you can name it something else, such as whoa:

i match {
  case 0 => println("1")
  case 1 => println("2")
  case whoa => println("You gave me: " + whoa)
}

It’s important to provide a default match. Failure to do so can cause a MatchError:

scala> 3 match {
     |   case 1 => println("one")
     |   case 2 => println("two")
     |   // no default match
     | }
scala.MatchError: 3 (of class java.lang.Integer)
many more lines of output ...