A common function-like interface for accessing information about attributes, based on the two core findAttr and convert methods.

Extenders can be fairly flexible. The value of an attribute is specified by the extender as type Info. Possibly-missing attributes are returned in type Holder, which should be parametrizable. For example, you could create an AttrHelper that deals in String attribute values (type Info = String) and returns Options in cases where the attribute may not be found.

Note that you can invoke an AttrHelper with conversion functions to turn an Info into an arbitrary type.

A sample implementation:

case class HtmlAttributes(in: Elem) extends AttrHelper[Box] {
  type Info = String

  def findAttr(key: String): Option[Info] = {
    in.attribute(key).map(_.text)
  }

  def findAttr(prefix: String, key: String): Option[Info] = {
    in.attribute(prefix, key).map(_.text)
  }

  def convert[T](in: Option[T]): Box[T] = Box(in)
}

The helper above takes a scala Elem and provides a series of ways to access the values of its elements. For example:

val attributes = HtmlAttributes(elem)

attributes("class") // class attribute as String, Empty if absent
attributes("lift", "bind") // as above with lift:bind attribute
attributes("class", "nothing") // class attribute, "nothing" if absent
attributes("lift", "bind", "nothing") // as above with lift:bind attribute
attributes("class", _.split(" ")) // class attribute as array, Empty if absent
attributes("lift", "bind", _.split(" ")) // as above with lift:bind attribute
attributes("class", _.split(" "), Array()) // class attribute as array, Array() if absent
attributes("lift", "bind", _.split(" "), Array()) // as above with lift:bind attribute