CODEWITHSUNDEEP
scalaplayframework-2.0loops
Mark
Mark

Reputation: 5499

Can't understand Iteratee.fold in Play 2.0

I'm reading the source code of Iteratee.scala: https://github.com/playframework/Play20/blob/master/framework/src/iteratees/src/main/scala/play/api/libs/iteratee/Iteratee.scala

Specifically the convenience method for constructing the "fold" iteratee. 

def fold[E, A](state: A)(f: (A, E) => A): Iteratee[E, A] = {
  def step(s: A)(i: Input[E]): Iteratee[E, A] = i match {

    case Input.EOF => Done(s, Input.EOF)
    case Input.Empty => Cont[E, A](i => step(s)(i))
    case Input.El(e) => { val s1 = f(s, e); Cont[E, A](i => step(s1)(i)) }
  }
  (Cont[E, A](i => step(state)(i)))
}

On each of the case statements, we are calling Done or Cont constructors. But where are these constructors defined? I infer that these must be implementors of the Iteratee trait but I couldn't find them by doing ctrl+F for "extends Iteratee."

Upvotes: 3

Views: 542

Answers (2)

senia
senia

Reputation: 38045

See docementation or source:

object Done {
/**
* Create an [[play.api.libs.iteratee.Iteratee]] in the “done” state.
* @param a Result
* @param e Remaining unused input
*/
  def apply[E, A](a: A, e: Input[E] = Input.Empty): Iteratee[E, A] = new Iteratee[E, A] {
    def fold[B](folder: Step[E, A] => Future[B]): Future[B] = folder(Step.Done(a, e))
  }
}

It's not a constructor. Done(s, Input.EOF) means Done.apply(s, Input.EOF). Same with Cont.

Upvotes: 4

helium
helium

Reputation: 1078

Done doesn't need to directly extend Iteratee. It could extend another class or trait which then extends Iteratee. You could search for class Cont and then follow the inheritance relationship from there.

Upvotes: -1

Related Questions