Make Stream transformation respect the single/multi subscriber nature of the source.

Make Stream transformation respect the single/multi subscriber nature of the source.

Add .isSingleSubscriber getter to Stream, and make use of it to create different streams for the transformations.

_ForwardingStreamTransformation is no longer itself a stream, but creates a stream depending on the source.

R=floitsch@google.com

Committed: https://code.google.com/p/dart/source/detail?r=17044

[floitsch, 2013-01-14 16:09:09]

LGTM.
But I'm thinking more and more that Streams should be constructed the same ways
as Iterables:

class WhereTransformer implements Stream {
  WhereTransformer(this._stream, this.predicate);
  listen(onData, onError, onDone) {
    var result = new WhereSubscription(this.predicate, onData, onError, onDone);
    _stream.listen(result._onData, result._onError, result._onDone));
  }
}

class WhereSubscription { ... }

Basically let the subscriptions do the actual work, as for the iterables.

https://codereview.chromium.org/11886013/diff/6/sdk/lib/async/stream.dart
File sdk/lib/async/stream.dart (right):

https://codereview.chromium.org/11886013/diff/6/sdk/lib/async/stream.dart#new...
sdk/lib/async/stream.dart:35: bool get isSingleSubscription;
different CL, but sometimes we have singleSubscriber, and sometimes
singleSubscription. We should be consistent.

https://codereview.chromium.org/11886013/diff/6/sdk/lib/async/stream.dart#new...
sdk/lib/async/stream.dart:124: * or simply return to make the stream forget the
error.
different CL: "if the error needs to be transformed into a value, use the [XYZ]
transformer."
Maybe just add a TODO for now?.

https://codereview.chromium.org/11886013/diff/6/sdk/lib/async/stream_impl.dart
File sdk/lib/async/stream_impl.dart (right):

https://codereview.chromium.org/11886013/diff/6/sdk/lib/async/stream_impl.dar...
sdk/lib/async/stream_impl.dart:546: bool get isSingleSubscription => false;
I don't think anybody wants to override this method :)
Move it above the comments.

[Lasse Reichstein Nielsen, 2013-01-15 07:19:50]

https://codereview.chromium.org/11886013/diff/6/sdk/lib/async/stream.dart
File sdk/lib/async/stream.dart (right):

https://codereview.chromium.org/11886013/diff/6/sdk/lib/async/stream.dart#new...
sdk/lib/async/stream.dart:124: * or simply return to make the stream forget the
error.
On 2013/01/14 16:09:09, floitsch wrote:
> different CL: "if the error needs to be transformed into a value, use the
[XYZ]
> transformer."
> Maybe just add a TODO for now?.

Done.

https://codereview.chromium.org/11886013/diff/6/sdk/lib/async/stream_impl.dart
File sdk/lib/async/stream_impl.dart (right):

https://codereview.chromium.org/11886013/diff/6/sdk/lib/async/stream_impl.dar...
sdk/lib/async/stream_impl.dart:546: bool get isSingleSubscription => false;
On 2013/01/14 16:09:09, floitsch wrote:
> I don't think anybody wants to override this method :)
> Move it above the comments.

Done.