What does `object Foo extends (Bar => Baz)` mean?

Question

I was reading dispatch's code, and come across this file, in which, it says:

object Elem extends (Res => scala.xml.Elem) {
  def apply(res: Res) =
    XML.withSAXParser(factory.newSAXParser).loadString(res.getResponseBody)
    ...

What does object Elem extends (Res => scala.xml.Elem) mean?

Answer 1

A => B is the syntax used to describe anonymous functions.

The object declaration

object Elem extends (Res => scala.xml.Elem) { /* ... */ }

is shorthand for

object Elem extends Function1[Res, scala.xml.Elem] { /* ... */ }

In natural language: Elem is a function which produces a scala.xml.Elem object from a Res object.

A look at the scaladoc for Function1 shows that Function1 declares an abstract apply method which is used to implement the function's logic.