Add Stream.empty.

Also iprove Future.value(null) and documentation of some Stream related classes.

R=sgjesse@google.com

Committed: https://github.com/dart-lang/sdk/commit/fbedc2b86f6b9df7e32d49d2b4a10e5cafb6d127

[Lasse Reichstein Nielsen, 2015-06-15 10:35:19]

lrn@google.com changed reviewers:
+ sgjesse@google.com

[Søren Gjesse, 2015-06-15 12:57:42]

lgtm

https://codereview.chromium.org/1177343004/diff/20001/sdk/lib/async/stream.dart
File sdk/lib/async/stream.dart (right):

https://codereview.chromium.org/1177343004/diff/20001/sdk/lib/async/stream.da...
sdk/lib/async/stream.dart:1528: * As [StreamConsumer.close], or as
[EventSink.close] that returns a future.
Not sure I understand this last line.

https://codereview.chromium.org/1177343004/diff/20001/tests/lib/async/stream_...
File tests/lib/async/stream_empty_test.dart (right):

https://codereview.chromium.org/1177343004/diff/20001/tests/lib/async/stream_...
tests/lib/async/stream_empty_test.dart:39: // Still not complete.
Add

  Expect.equals(tick, 1);

here as well.

https://codereview.chromium.org/1177343004/diff/20001/tests/lib/async/stream_...
tests/lib/async/stream_empty_test.dart:51: // Doesn't complete while paused.
Wrong comment.

[sra1, 2015-06-15 16:17:40]

sra@google.com changed reviewers:
+ sra@google.com

[sra1, 2015-06-15 16:17:41]

https://codereview.chromium.org/1177343004/diff/20001/sdk/lib/async/future.dart
File sdk/lib/async/future.dart (right):

https://codereview.chromium.org/1177343004/diff/20001/sdk/lib/async/future.da...
sdk/lib/async/future.dart:184: if (value == null) return _nullFuture;
What is the purpose of this change?

I think this will make

  new Future<int>.value(null) is Future<String>  -->  true

The change will also break under the stricter type checking of DDC, so will end
up being reverted when the DDC copy of the libraries is merged back.

[Lasse Reichstein Nielsen, 2015-06-15 16:24:42]

https://codereview.chromium.org/1177343004/diff/20001/sdk/lib/async/future.dart
File sdk/lib/async/future.dart (right):

https://codereview.chromium.org/1177343004/diff/20001/sdk/lib/async/future.da...
sdk/lib/async/future.dart:184: if (value == null) return _nullFuture;
Ack, true.
The purpose is entirely to save some space and not create extra objects for
null-futures when they aren't needed. But you are right, it breaks typing. 

We probably don't want to do `if (value == null && T == dynamic)...`.

[sra1, 2015-06-15 16:29:22]

On 2015/06/15 16:24:42, Lasse Reichstein Nielsen wrote:
>
https://codereview.chromium.org/1177343004/diff/20001/sdk/lib/async/future.dart
> File sdk/lib/async/future.dart (right):
> 
>
https://codereview.chromium.org/1177343004/diff/20001/sdk/lib/async/future.da...
> sdk/lib/async/future.dart:184: if (value == null) return _nullFuture;
> Ack, true.
> The purpose is entirely to save some space and not create extra objects for
> null-futures when they aren't needed. But you are right, it breaks typing. 
> 
> We probably don't want to do `if (value == null && T == dynamic)...`.

We certainly don't want to do T == dynamic.  That would defect the type erasure
optimization by using T and so demanding T is carried.  (Many things defeat the
type erasure optimization, but try not to add more)

[Lasse Reichstein Nielsen, 2015-06-16 09:25:12]

ptal

https://codereview.chromium.org/1177343004/diff/20001/sdk/lib/async/future.dart
File sdk/lib/async/future.dart (right):

https://codereview.chromium.org/1177343004/diff/20001/sdk/lib/async/future.da...
sdk/lib/async/future.dart:184: if (value == null) return _nullFuture;
Rolling this change back.

https://codereview.chromium.org/1177343004/diff/20001/sdk/lib/async/stream.dart
File sdk/lib/async/stream.dart (right):

https://codereview.chromium.org/1177343004/diff/20001/sdk/lib/async/stream.da...
sdk/lib/async/stream.dart:1528: * As [StreamConsumer.close], or as
[EventSink.close] that returns a future.
Reworded.

https://codereview.chromium.org/1177343004/diff/20001/tests/lib/async/stream_...
File tests/lib/async/stream_empty_test.dart (right):

https://codereview.chromium.org/1177343004/diff/20001/tests/lib/async/stream_...
tests/lib/async/stream_empty_test.dart:39: // Still not complete.
On 2015/06/15 12:57:42, Søren Gjesse wrote:
> Add
> 
>   Expect.equals(tick, 1);
> 
> here as well.

Done.

https://codereview.chromium.org/1177343004/diff/20001/tests/lib/async/stream_...
tests/lib/async/stream_empty_test.dart:51: // Doesn't complete while paused.
Fixed.

[Søren Gjesse, 2015-06-16 09:27:05]

lgtm

[Lasse Reichstein Nielsen, 2015-06-16 09:38:46]

Committed patchset #3 (id:40001) manually as
fbedc2b86f6b9df7e32d49d2b4a10e5cafb6d127 (presubmit successful).

[kevmoo, 2015-06-30 21:27:30]

On 2015/06/16 09:38:46, Lasse Reichstein Nielsen wrote:
> Committed patchset #3 (id:40001) manually as
> fbedc2b86f6b9df7e32d49d2b4a10e5cafb6d127 (presubmit successful).

Please update CHANGELOG.md for API changes.