Scala Cookbook

20.4. Use Match Expressions and Pattern Matching

Problem

Match expressions (and pattern matching) are a major feature of the Scala programming language, and you want to see examples of the many ways to use them.

Solution

Match expressions (match/case statements) and pattern matching are a major feature of the Scala language. If you’re coming to Scala from Java, the most obvious uses are:

• As a replacement for the Java switch statement

• To replace unwieldy if/then statements

However, pattern matching is so common, you’ll find that match expressions are used in many more situations:

• In try/catch expressions

• As the body of a function or method

• With the Option/Some/None coding pattern

• In the receive method of actors

The following examples demonstrate these techniques.

Replacement for the Java switch statement and unwieldy if/then statements

Recipe 3.8 showed that a match expression can be used like a Java switch statement:

val month = i match {
  case 1  => "January"
  case 2  => "February"

  // more months here ...

  case 11 => "November"
  case 12 => "December"
  case _  => "Invalid month"  // the default, catch-all
}

It can be used in the same way to replace unwieldy if/then/else statements:

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

These are simple uses of match expressions, but they’re a good start.

In try/catch expressions

It helps to become comfortable with match expressions, because you’ll use them with Scala’s try/catch syntax. The following example shows how ...