IAsyncEnumerable without Await

[TonyValenti]

What is the right way to implement an IAsyncEnumerable that doesn't actually await anything so that you don't get any warnings?

[CyrusNajmabadi]

can you provide more details (including code)? I don't know what warnings you're referring to.

[CyrusNajmabadi]

public abstract class Foo2 : Foo
{
#pragma warning disable CS1998 // Async method lacks 'await' operators and will run synchronously
    public override async IAsyncEnumerable<int> DoWorkAsync()
#pragma warning restore CS1998 // Async method lacks 'await' operators and will run synchronously
    {
        yield return 1;
    }
}

[TonyValenti]

Is there a way to do it without disabling the warning?

[TonyValenti]

I tried yield return Task.FromResult(1) and that didnt' do it either.

[RikkiGibson]

ping @jcouv in case you have any suggestions for this scenario :)

[colejohnson66]

Can you just remove the async qualifier?

[jcouv]

Options I can think of:

1. Cheapest way is to include an await Task.CompletedTask; in your code
2. Implementing an adapter type by hand (your own types implementing IAsyncEnumerable and IAsyncEnumerator, which would wrap around an IEnumerator), which is a bit tedious
3. Find a library that already implemented such wrapper types
4. Raise the question on StackOverflow and see if any better ideas come up ;-)

[Jason5Lee]

You can add await Task.Yield() before yield return .

[HaloFour]

await Task.CompletedTask; would be more efficient since the awaiter is already completed so the method will continue synchronously. Task.Yield() yields the thread and posts the continuation to the synchronization context or thread pool.

But yeah, the theory is the same. Awaiting on anything will silence the warning. It would be nice if there was a helper for this, like a way to wrap a scalar T into an IAsyncEnumerable<T>.

[Richiban]

Like a Task.FromResults, for example? A naive implementation might look like:

    public async IAsyncEnumerable<T> FromResults<T>(params T[] items)
    {
        await Task.CompletedTask;
        
        foreach (var item in items)
        {
            yield return item;
        }
    }

[silkfire]

You can put the statement at the end of your method:

public async IAsyncEnumerable<T> FromResults<T>(params T[] items)
{
   foreach (var item in items)
   {
      yield return item;
   }

   await Task.CompletedTask;
}