Scala pattern matching syntax

6
votes

I've been playing with scala pattern matching recently and was wondering whether there is a way to create an extractor inside of the case statement. The following code works, but you have to define the extractor first and assign it to a val:

val Extr = "(.*)".r
"test" match {
  case Extr(str) => println(str)
}

What I would like to do, or what I would like someone to confirm is impossible, is something like this:

"test" match {
  case ("(.*)".r)(str) => println(str)
}

EDIT: In case anyone from the scala team is reading this: Would it be feasible to implement this?

2
scalasyntaxpattern-matching
+1 for the suggestion! This would be useful indeed in other cases. - Jean-Philippe Pellet
@JPP: Indeed. The case I was originally thinking of was that of or and and as library functions to build complex extractors from simpler ones. - Kim Stebel
See also stackoverflow.com/questions/2411573/… - Knut Arne Vedaa

2 Answers

5
votes

Unfortunately it is not possible and I see no way to simplify your first example.

The case statement has to be followed by a Pattern. The Scala Language Specification shows the BNF of patterns in section 8.1. The grammar of patterns is quite powerful, but is really just a pattern, no method calls or constructors are allowed there.

0
votes

I had a similar problem and i solved it like this:

case x if x.matches("regex") => foo(x)

I don't know if this is exactly what you want, but it works