If transformException() returns a future, act like chain().

If transformException() returns a future, act like chain().

Committed: https://code.google.com/p/dart/source/detail?r=12661

[Siggi Cherem (dart-lang), 2012-09-20 22:00:17]

lgtm

https://codereview.chromium.org/10958021/diff/1/lib/coreimpl/future_implement...
File lib/coreimpl/future_implementation.dart (right):

https://codereview.chromium.org/10958021/diff/1/lib/coreimpl/future_implement...
lib/coreimpl/future_implementation.dart:231: result.then((value) =>
completer.complete(value));
I've seen the pattern of the last 4 lines quite a few times, could we add a
helper method to do this? (it could be private, for instance:

class Completer<T> {
  _propagateFrom(Future<T> future) {
    future.handleException((e) {
      completeException(e, future.stackTrace);
      return true;
    });
    future.then((value) => complete(value));
  }
}

or maybe better as part of future?

class Future<T> {
  ...
  _forwardTo(Completer<T> completer) {
    handleException((e) {
      completer.completeException(e, stackTrace);
      return true;
    });
    then((value) => completer.complete(value));
  }
}

[Bob Nystrom, 2012-09-20 22:34:53]

Thanks!

https://codereview.chromium.org/10958021/diff/1/lib/coreimpl/future_implement...
File lib/coreimpl/future_implementation.dart (right):

https://codereview.chromium.org/10958021/diff/1/lib/coreimpl/future_implement...
lib/coreimpl/future_implementation.dart:231: result.then((value) =>
completer.complete(value));
On 2012/09/20 22:00:17, sigmund wrote:
> I've seen the pattern of the last 4 lines quite a few times, could we add a
> helper method to do this? (it could be private, for instance:
> 
> class Completer<T> {
>   _propagateFrom(Future<T> future) {
>     future.handleException((e) {
>       completeException(e, future.stackTrace);
>       return true;
>     });
>     future.then((value) => complete(value));
>   }
> }
> 
> or maybe better as part of future?
> 
> class Future<T> {
>   ...
>   _forwardTo(Completer<T> completer) {
>     handleException((e) {
>       completer.completeException(e, stackTrace);
>       return true;
>     });
>     then((value) => completer.complete(value));
>   }
> }

Done.

I put it in _FutureImpl (which, by the way, should just be unified with Future
at some point after M1) and it passes in the future explicitly (instead of using
'this'). I can't put it in Future because you can't rely on a private method
existing on an object other than this. If you do:

foo(Future bar) {
  bar._somePrivateMethod();
}

It's possible that the bar that gets passed in is an instance of some other type
that implements Future's implicit interface and doesn't have _somePrivateMethod.

[Siggi Cherem (dart-lang), 2012-09-20 22:37:25]

lgtm! thanks!