Scala Cookbook

3.9. Assigning the Result of a Match Expression to a Variable

Problem

You want to return a value from a match expression and assign it to a variable, or use a match expression as the body of a method.

Solution

To assign a variable to the result of a match expression, insert the variable assignment before the expression, as with the variable evenOrOdd in this example:

val evenOrOdd = someNumber match {
  case 1 | 3 | 5 | 7 | 9 => println("odd")
  case 2 | 4 | 6 | 8 | 10 => println("even")
}

This approach is commonly used to create short methods or functions. For example, the following method implements the Perl definitions of true and false:

def isTrue(a: Any) = a match {
  case 0 | "" => false
  case _ => true
}

You’ll hear that Scala is an “expression-oriented programming (EOP) language,” which Wikipedia defines as, “a programming language where every (or nearly every) construction is an expression and thus yields a value.” The ability to return values from if statements and match expressions helps Scala meet this definition.

See Also

• Recipe 20.3

• The Expression-Oriented Programming page on Wikipedia