/// <summary>
/// Return all text lines (accompanied by source numbers) for a given feeder.
/// </summary>
/// <param name="feeder"></param>
/// <returns></returns>
private IEnumerable <Tuple <ExternalLine, int> > GetAllLines(LineFeederForSource feeder)
{
Tuple <ExternalLine, int> line;
while ((line = feeder.GetNextLine()) != null)
{
yield return(line);
}
}
/// <summary>
/// Return sequence of tasks with all text lines (accompanied by source numbers) for a given feeder.
/// The sequence has an extra EOD element (null) at end.
/// </summary>
/// <param name="feeder"></param>
/// <returns></returns>
private IEnumerable <Task <Tuple <ExternalLine, int> > > GetAsyncAllLines(LineFeederForSource feeder)
{
while (true)
{
var linePlus = feeder.GetNextLineAsync();
yield return(linePlus);
//Note that yield cannot be combined with await (hence we need the feeder to return the entire value to be returned, i.e. the tuple).
//For this reason, the Task returned from GetNextLineAsync (unlike return value from synchronous GetNextLine) provides no clue
// as to whether it was the last value (null) or not; this can only be determined after the async call completes, i.e.
// after the tasks's result becomes available. Therefore, the sequence returned by this method contains the EOD mark (tuple with null),
// which is unlike the "synchronous" GetAllLines method (which removes the EOD mark that terminates the sequence).
//Note that the Result below will not block (as long as the consumer of this method processes the task result before requesting next item).
if (linePlus.Result.Item1 == null)
{
yield break;
}
//Also note that System.Interactive.Async (Ix Async) package might be helpful in elimination of sending the tuples containing nulls.
}
}