Does Scala have a library method to build Option-s that takes into account empty strings?

Question

I want to filter out empty strings to put them into an Option. So I quickly built this now:

def StrictOption(s: String) = s match {
  case s if s != null && s.trim.length() > 0 => Some(s)
  case _ => None
}

Question: is this maybe already somewhere in the standard library?

Answer 1

I don't think there's one single method in the standard library to do this, but you can do this much more tersely than your implementation.

Option(s).filter(_.trim.nonEmpty)

Answer 2

If you care at all about performance then

if (s.trim.isEmpty) None else Some(s)

is only 4 characters longer than Ben James's solution, and runs 3 times faster, in my benchmark (47 vs 141).

Answer 3

Starting Scala 2.13, for those not expecting nulls (non-Java context), Option::unless and Option::when are now an alternative option:

// val str = "hello"
Option.unless(str.isEmpty)(str)
// Option[String] = Some(hello)
Option.when(str.nonEmpty)(str)
// Option[String] = Some(hello)

// val str: String = ""
Option.unless(str.isEmpty)(str)
// Option[String] = None
Option.when(str.nonEmpty)(str)
// Option[String] = None

Answer 4

There's nothing built in; Ben's filter is the best brief version if performance isn't an issue (e.g. you're validating user input). Typically, performance will not be an issue.

Also, note that it's a little strange to use match when you're not actually matching anything; it's just more boilerplate to get an if-else statement. Just say

if (s ne null && s.trim.length > 0) Some(s) else None

which is about as fast and brief as anything, unless you want to write your own is-it-whitespace method. Note that trim uses a peculiar criterion: anything above \u0020 (i.e. ' ') is not trimmed, and anything equal or below is. So you could also write your own trimmed-string-is-empty detector, if performance of this operation was particularly important:

def ContentOption(s: String): Option[String] = {
  if (s ne null) {
    var i = s.length-1
    while (i >= 0) {
      if (s.charAt(i) > ' ') return Some(s)
      i -= 1
    }
  }
  None
}