Question

I have the following code:

val z: String = tree.symbol.toString
z match {
  case "method +" | "method -" | "method *" | "method ==" =>
    println("no special op")
    false
  case "method /" | "method %" =>
    println("we have the special div operation")
    true
  case _ =>
    false
}

Is it possible to create a match for the primitive operations in Scala:

"method *".matches("(method) (+-*==)")

I know that the (+-*) signs are used as quantifiers. Is there a way to match them anyway?
Thanks from a avidly Scala scholar!

Answer 1

Sure.

val z: String = tree.symbol.toString
val noSpecialOp = "method (?:[-+*]|==)".r
val divOp = "method [/%]".r
z match {
  case noSpecialOp() =>
    println("no special op")
    false
  case divOp() =>
    println("we have the special div operation")
    true
  case _ =>
    false
}

Things to consider:

• I choose to match against single characters using [abc] instead of (?:a|b|c).
• Note that - has to be the first character when using [], or it will be interpreted as a range. Likewise, ^ cannot be the first character inside [], or it will be interpreted as negation.
• I’m using (?:...) instead of (...) because I don’t want to extract the contents. If I did want to extract the contents — so I’d know what was the operator, for instance, then I’d use (...). However, I’d also have to change the matching to receive the extracted content, or it would fail the match.
• It is important not to forget () on the matches — like divOp(). If you forget them, a simple assignment is made (and Scala will complain about unreachable code).
• And, as I said, if you are extracting something, then you need something inside those parenthesis. For instance, "method ([%/])".r would match divOp(op), but not divOp().