pattern matching - How to suppress "match is not exhaustive!" warning in Scala

Question

How can I suppress the "match is not exhaustive!" warning in the following Scala code?

val l = "1" :: "2" :: Nil
l.sliding(2).foreach{case List(a,b) => }

The only solution that I found so far is to surround the pattern matching with an additional match statement:

l.sliding(2).foreach{x => (x: @unchecked) match {case List(a,b) => }}

However this makes the code unnecessarily complex and pretty unreadable. So there must be a shorter and more readable alternative. Does someone know one?

Edit

I forgot to mention that my list l has at least 2 elements in my program. That's why I can safely suppress the warning.

Answer 1

Here are several options:

1. You can match against Seq instead of List, since Seq doesn't have the exhaustiveness checking (this will fail, like your original, on one element lists):

   l.sliding(2).foreach{case Seq(a, b) => ... }
   

2. You can use a for comprehension, which will silently discard anything that doesn't match (so it will do nothing on one element lists):

   for (List(a, b) <- l.sliding(2)) { ... }
   

3. You can use collect, which will also silently discard anything that doesn't match (and where you'll get an iterator back, which you'll have to iterate through if you need to):

   l.sliding(2).collect{case List(a,b) => }.toList