What is the reference of the object that a partial function matches on?

Looking at this function as an example:

def receive = {
  case "test" => log.info("received test")
  case _      => log.info("received unknown message")
}

What object is being matched on? On the right hand side of the arrows, how can I refer to the object being matched on?

Solution

You can do it with an if-guard:

def receive: String => Unit = {
  case str if str == "test" => println(str)
  case _ => println("other")
}

Option("test").map(receive) // prints "test"
Option("foo").map(receive) // prints "other"

Note that if you have an object that you want to refer to, then stuff like e.g. foo: Foo(s) won't work (foo: Foo will, but then you lose the reference to Foo's value s). In that case you need to use the @ operator:

case class Foo(s: String)

def receive: Foo => Unit = {
  case foo@Foo(s) => println(foo.s) // could've referred to just "s" too
  case _ => println("other")
}

Option(Foo("test")).map(receive) // prints "test"