An example from lift cookbook, the pattern matching is bit curious here.
serve("issues" / "by-state" prefix { case "open" :: Nil XmlGet _ => <p>None open</p> case "closed" :: Nil XmlGet _ => <p>None closed</p> case "closed" :: Nil XmlDelete _ => <p>All deleted</p> }) I don't understand what the XmlGet _ part is doing. Could anyone explain a bit?
One of Scala's nice niche features is that many binary operations (e. g. f(x, y)) can be invoked from the infix position x f y. This applies to normal method calls:
case class InfixMethodCalls(x: Int) { def wild(y: Int): Int = x + y } val infix = InfixMethodCalls(3) infix wild 4 type constructors:
// A simple union type based on http://www.scalactic.org/ trait Or[A, B] case class Good[A, B](value: A) extends Or[A, B] case class Bad[A, B](value: B) extends Or[A, B] def myMethod(x: Int Or String): Int // This is the same as def myMethod(x: Or[Int, String]): Int and unapply / unapplySeq:
object InfixMagic { def unapply(x: Any) = Option((List(x), x)) } 123 match { case v :: Nil InfixMagic x => println(s"got v: $v and x: $x") } // is the same as 123 match { case InfixMagic(v :: Nil, x) => println(s"got v: $v and x: $x") } So in the case of XmlGet this syntax here:
case "open" :: Nil XmlGet _ => is the same as:
case XmlGet("open" :: Nil, _) => And the _ is ignoring the Req parameter, which is the second part of the returned value from TestGet.unapply.
If you go through RuleHelper class of liftweb framework one will be able to make few assumptions.
XmlGet and XmlDelete extends TestGet trait with unapply method and Request argument. So this part basically means: check if it's XmlGet\XmlDelete method with any request.
How list is separated from second part? Good question. Suppose implicit listStringToSuper and listServeMagic used for this purpose.
_ :: Nil.