If, Else, and Match in Scala

Scala improves upon basic conditional statements in a number of ways. Here are a few of the main points in understanding how to write conditional statements in Scala.

If Statements

If expressions have values. This is actually a very useful mechanism. Similar to the last statement in a function, an if-else statement returns the value of the expression that follows the if-else. For example, the following if-statement has a value of true or false depending on the value of x.

if (x < 10) true else false

You can actually initialize a variable with the result of this expression if you want.

val result = if (x < 10) {
   true
}
else {
   false
}


Match Statements

We don't have traditional switch-case statements in Scala, but to no surprise, there's something even better. Scala's "match" expressions are an improved switch statement. Here's an example of a "match" expression that sets the value of a variable "n" based on the value of a variable named "number". If number is 0, then n becomes "zero". If number is 1, then n becomes "one". If number is any other value, then n becomes "some other value".

val n = number match {
   case 0 => "zero"
   case 1 => "one"
   case _ => "some other value"
}

There's no ability for fall-through to occur, like can often happen in a traditional switch statement. Rarely, do you want fall-through, but if you do need to have a range of values evaluate to the same result, you can do that with a "guard". For example, we can modify our match expression to match values of 0, 1, 10-20, and 30-50. Anything else is caught with our "case _" and will result in a value of "some other value". The guard can be any Boolean condition.

val n = number match {
  case 0 => "zero"
  case 1 => "one"
  case num if 10 until 20 contains num => "between ten and twenty"
  case num if 30 until 50 contains num => "between thirty and fifty"
  case _ => "some other value"
}