CODEWITHSUNDEEP
scalapattern-matchingmatchcase
ideaboxer
ideaboxer

Reputation: 4091

Multiple pattern matches with same input variable

I oftentimes face the following problem:

val b = a match {
  case Some(a) => "1"
  case None => "n"
}
val c = a match {
  case Some(a) => "2"
  case None => "n"
}

Obviously, the match is executed twice even though it is only necessary once. How can I make sure the compiler takes this into account?

Upvotes: 1

Views: 271

Answers (2)

Rex Kerr
Rex Kerr

Reputation: 167891

Matches can be extremely fast--comparable to an if-statement. Don't worry about doing the work twice unless it's a difficult match.

It's slightly easier to match a default than another case, so if you really don't need the parameter your best bet is

val b = a match { case None => "n"; case _ => "1" }
val c = a match { case None => "n"; case _ => "2" }

This will often even outperform a mutable solution like

var b,c = "n"
a match { case Some(_) => b = "1"; c = "2"; case _ => }

and will certainly outperform any tuple-creation.

If the match is a time-consuming one then you have to store your results and return them in a tuple or other suitable data structure, as om-nom-nom has already demonstrated. This may also be more clear, depending on context.

Upvotes: 1

om-nom-nom
om-nom-nom

Reputation: 62835

I don't think there will be any performance gain but you can write your code like this: 

val (b, c) = a match {
  case Some(a) => ("1","2)
  case None => ("n", "n")
}

Upvotes: 8

Related Questions