[Proposal]: await using and ConfigureAwait without going back to pre C# 8 indentation

[virzak]

[Proposal]: await using and ConfigureAwait without going back to pre C# 8 indentation

• Proposed
• Prototype: Not Started
• Implementation: Not Started
• Specification: Not Started

Summary

Allow C# 8 using declaration with await using and .ConfigureAwait(false)

Current syntax:

var c = new MyAsyncDisposableClass();
await using (c.ConfigureAwait(false))
{
    ...
}

Proposed syntax:

var c = new MyAsyncDisposableClass();
await using c.ConfigureAwait(false);
...

Motivation

With release of C# 8, most using blocks were converted to using declarations. It was great for removing unnecessary indentation.

IAsyncDisposable a less advertised feature and didn't prominently feature in samples until later. Here is a recent commit where EF Core samples changed to await using.

Our project, which creates a lot of DbContext and FileStream instances benefitted from reducing indentation. The using statement usually occurs once per method. ConfigureAwait FAQ's example of .ConfigureAwait extension on IAsyncDisposable takes the project back to the old indentation.

Detailed design

Drawbacks

Alternatives

Unresolved questions

Not sure how important it is to use the ConfigureAwait extension, since the EF Core sample doesn't use it and there is no compiler / analyzer warning if omitted.

Design meetings

[svick]

Note that you can write the code like this:

await using var _ = c.ConfigureAwait(false);

(This actually declares a variable named _, it's not a discard.)

Also, I think this is pretty much a duplicate of #2235.

[virzak]

@svick, yep that works.