Scala : how to expose regex variables bound within a case statement - regex

Question

Scala regex works great under either of two conditions:
unconditionally executed code:
e.g.
val lineregx = """([\w]+)\t([/\w.+-]+)\t([/\w+=\-!%# ]+)""".r
val anotherregx = """([\w]+)\t([/\w+=\-!%# ]+)""".r
val lineregx(category, aaUrl, title)
or if inside a case statement we consume the expressions (and don't need them again..)
val lineregx = """([\w]+)\t([/\w.+-]+)\t([/\w+=\-!%# ]+)""".r
line match {
case lineregx(category, aaUrl, title) => // do something with category, aaUrl and title in here!
case anotherRegx(category, aaUrl) => // do something different with category, aaUrl and title in here!
case _ => { println("did not match line %s".format(line)); return 0 }
}
But what about if i need to 'surface' the matches to variables outside of the case statement? Specifically the var's shown below,
val lineregx = """([\w]+)\t([/\w.+-]+)\t([/\w+=\-!%# ]+)""".r
var category = "" ; var aaUrl = "";var title = ""
line match {
case lineregx(category, aaUrl, title) => val lineregx(category, aaUrl, title) = line
case anotherRegx(category, aaUrl) => val lineregx(category, aaUrl) = line
case _ => { println("did not match line %s".format(line)); return 0 }
}
// Do something with category, aaUrl, title HERE after the case statement.
Problem is , the syntax for applying the lineregx/anotherregex makes those variables local to the case statement only.

Answer 1

Roughly,
val lineregx = """([\w]+)\t([/\w.+-]+)\t([/\w+=\-!%# ]+)""".r
val (category, aaUrl, title) = line match {
case lineregx(category, aaUrl, title) => (category, aaUrl, title)
case anotherRegx(category, aaUrl) => (category, aaUrl, ???)
case _ => { println("did not match line %s".format(line)); return 0 }
}
// Do something with category, aaUrl, title HERE after the case statement.
But that code is quite disorganized. For one thing, there's the question of the value of title for the second case. For another, there's the early return. Instead, the code would probably be best organized like this:
// method declaration
// ...
val lineregx = """([\w]+)\t([/\w.+-]+)\t([/\w+=\-!%# ]+)""".r
line match {
case lineregx(category, aaUrl, title) => f(category, aaUrl, title)
case anotherRegx(category, aaUrl) => f(category, aaUrl, ???)
case _ =>
println("did not match line %s".format(line))
0
}
} // end of method
def f(category: String, aaUrl: String, title: String): Int = {
// Do something with category, aaUrl, title HERE
}

Answer 2

You could use Option:
val lineregx = """([\w]+)\t([/\w.+-]+)\t([/\w+=\-!%# ]+)""".r
val (maybeCat, maybeUrl, maybeTitle) =
line match {
case lineregx(category, aaUrl, title) => (Some(category), Some(aaUrl), Some(title))
case anotherRegx(category, aaUrl) => (Some(category), Some(aaUrl), None)
case _ =>
println("did not match line %s".format(line))
(None, None, None)
}
var category = maybeCat getOrElse ""
var aaUrl = maybeURL getOrElse ""
var title = maybeTitle getOrElse ""
Slightly more verbose, but this way you can get the variables in the same scope.