A return statement should not be required in an async method

[kevmoo]

Future fuze() async {
  await new Future.value();
}

Expected:

no hint/error. This is a valid async method.

Actual:
Hint: This function declares a return type of 'Future', but does not end with a return statement

[DartBot]

This comment was originally written by @seaneagan

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As with issue #22092, it would have been nice to be able to do:

void fuze() async {
  await new Future.value();
}

[DartBot]

This comment was originally written by @mezoni

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As in Ruby???

def name
  my_name
end

How this can be related to current Dart syntax?

===========
The return statement returns a result to the caller of a synchronous function,
completes the future associated with an asynchronous function or terminates the
stream or iterable associated with a generator (9).
===========

You propose remove the following rule?

===========
Otherwise the return statement is executed by executing the statement
return null;
===========

As with issue #22092, it would have been nice to be able to do:

void fuze() async {
  await new Future.value();
}

Believe me it is not good.

[bwilkerson]

Added Priority-High label.

[DartBot]

This comment was originally written by @Emasoft

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An async method should NEVER have void as return type! Async void is EVIL. It is a 'fire and forget' insanely dangerous thing. It is the worst language design feature since "goto" (and incidentally for very similar reasons!). It's a well known language design error known to cause only bugs, all almost impossible to track. We suffered enough pain for it in C#, where the very designer of the language admitted the error. Please don't do the same error in Dart. We discussed the problem before here: https://code.google.com/p/dart/issues/detail?id=104

[DartBot]

This comment was originally written by @seaneagan

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I'm not sure why "async void" in C# is "fire and forget", but using a "void" return type for "async" methods in dart would be nothing like that.

This:

void foo async {
  await new Future.value();
}

would be the same as:

Futre<Null> foo async {
  await new Future.value();
}

except that it would validate (as much as is possible in a dynamically typed language) that the completion value of the future is not used.

Since using async is just supposed to be an implementation detail though, it would need to be possible to write methods which return Future<void> without using async, which is issue #2231.

[DartBot]

This comment was originally written by @Emasoft

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@seaneagan1 wrote:

I'm not sure why "async void" in C# is "fire and forget"

Have you read the linked issue #104? Or this article?
http://www.jayway.com/2012/10/07/asyncawait-in-c-a-disaster-waiting-to-happen/

[DartBot]

This comment was originally written by @seaneagan

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Yes, I agree that is something that an "extract method" refactoring should handle when code containing an await is extracted from an async method.

But it's unrelated to the proposal here for Future<void>, which would signify that the completion value of the future cannot be used, not that the returned Future cannot be awaited as is apparently the case with C#.

[stereotype441]

Set owner to @stereotype441.
Added Started label.

[stereotype441]

Fixed in revision 43361.

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Added Fixed label.

[kevmoo]

Dart VM version: 1.9.0-dev.6.0

Thanks!

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Added Verified label.

[kevmoo]

This seems to have regressed

Dart VM version: 1.9.0-dev.7.1

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Attachment:
[Screen Shot 2015-02-09 at 9.50.48 AM.png](https://storage.googleapis.com/google-code-attachments/dart/issue-22091/comment-12/Screen Shot 2015-02-09 at 9.50.48 AM.png) (37.15 KB)

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Added Triaged label.

[stereotype441]

I'm investigating.

[kevmoo]

False alarm: this is still fixed, but not pack-ported to the Java analyzer

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Added Fixed label.

[levrik]

@kevmoo Still getting this error displayed in Android Studio with the latest Dart plugin and Dart 2. Compiles fine though.