Scala | Programming | Functional Programming When You Do Want None February 25, 2015

Neil Chaudhuri (He/Him)

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In the applications I typically develop, I only care when strings are meaningful or when they aren’t because they are null (or nil, None, or Null depending on the language). Empty strings and strings containing only whitespace are this weird, in-between third category I really would prefer not to deal with. When I go to McDonald’s, I want to focus on the burgers and fries. I want absolutely nothing to do with the Filet-O-Fish.

Scala’s Option gives us a neat way to avoid meaningless strings if we wish.

I have blogged about Option before. It helps us avoid null in an elegant, typesafe way at compile-time. The collection-like semantics of Option helps us turn Some(meaninglessString) into None (not to be confused with Python’s None) so we can deal with it as if it were an organic None value.

It’s really pretty easy.

val option: Option[String] = Some("") 
//or Some("Vidya"), Some("   "), None, or whichever Option[String] you want
val result: String = option
  .filter(_.trim.nonEmpty)
  .map(string => s"You found a meaningful string $string")
  .getOrElse("You found None or an empty or whitespace-only string.")
println(result)

If you know Scala, you can see exactly what happens here. Check out that call to filter. We typically associate it with collections where filter removes all elements from the collection that don’t pass the condition. Option offers an analogous filter that returns None if the value “inside” Some doesn’t pass the condition. In the case of an empty or whitespace-only string, trimming it keeps it or makes it empty, so the filter test doesn’t pass and yields None. This is a really concise way of letting us deal with only two categories of strings—meaningful or not—instead of three. One place where this could come in handy is backend form validation of mandatory fields in web applications.

If you have the luxury of not having to distinguish between empty-ish strings and null, keep this tip in mind. Unless you’re Sir Mix-A-Lot, you actually might want None.