Is it possible to make non-capturing groups work in scala regexes when pattern matching

Question

As far as I can see from the docs, non-capturing groups are defined by (:? ), as in Java. (I believe it's the same underlying library). However, this doesn't seem to work: ``` var R = "a(:?b)c".r R.findFirstMatchIn("abc").get.group(1) ``` returns "b" (when it should be empty). I suspect this is not normally a problem, but when doing pattern matching, it means that I can't now do: ``` "abc" match {case R => println("ok");case _ => println("not ok")} > not ok ``` I have to do: ``` "abc" match {case R(x) => println("ok");case _ => println("not ok")} > ok ``` Is there any way to make this work "as expected"?

Accepted Answer

In addition to the correct answer, use val and parens:

```
scala> val R = "a(?:b)c".r  // use val
R: scala.util.matching.Regex = a(?:b)c

scala> "abc" match {case R() => println("ok");case _ => println("not ok")} // parens not optional
ok
```

You can also always use the wildcard sequence and not care whether you specified capturing groups. I discovered this recently and find it is most clear and robust.

```
scala> "abc" match {case R(_*) => println("ok");case _ => println("not ok")} 
ok
```

If anything matches, `_*` will, including an extractor returning `Some(null)`.

Is it possible to make non-capturing groups work in scala regexes when pattern matching

Solution

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