Prefer headOption to Head in Scala Collections

The List.head() method in Scala’s List collection class provides a simple way to get the first element in the list, but if the list is empty it will throw this exception (since there is nothing it can actually return)

val users: List[String] = loadLatestUsers()
val latestUser: String = users.head

java.util.NoSuchElementException: head of empty list
    at scala.collection.immutable.Nil$.head(List.scala:371)
    at scala.collection.immutable.Nil$.head(List.scala:368)
    ...

You can prevent this by checking that the list is non-empty before calling this method. A better (and more Scala-ish) way is to instead call List.headOption() which uses Scala’s Option pattern.

How to handle the case of an empty list depends on your requirements and context, especially what you plan[ned] to do with the first element of the list. If you can defer handling the empty list until the value is used, keep the Option wrapper around the element.

val latestUser: Option[String] = users.headOption

Or does an empty list denote a state so broken that you cannot continue?

val latestUser: String = users.headOption.getOrElse {
  throw new RuntimeException("No names are available!") )
}

Does an empty list make the rest of the method simply irrelevant?

val latestUser: String = users.headOption.getOrElse( return )

Or can a default, placeholder value be safely used here?

val latestUser: String = users.headOption.getOrElse( "" )

After using List.headOption to explicitly handle the case of an empty list, you have now prevented a potential failure at runtime with minimal changes or bulk added to your code.