Is it possible to “await yield return DoSomethingAsync()”

Question

Are regular iterator blocks (i.e. \"yield return\") incompatible with \"async\" and \"await\"?

This gives a good idea of what I\'m trying to do:

asyn         


        

Answer 1

This feature will be available as of C# 8.0. https://blogs.msdn.microsoft.com/dotnet/2018/11/12/building-c-8-0/

From MSDN

Async streams

The async/await feature of C# 5.0 lets you consume (and produce) asynchronous results in straightforward code, without callbacks:

async Task GetBigResultAsync()
{
    var result = await GetResultAsync();
    if (result > 20) return result; 
    else return -1;
}

It is not so helpful if you want to consume (or produce) continuous streams of results, such as you might get from an IoT device or a cloud service. Async streams are there for that.

We introduce IAsyncEnumerable, which is exactly what you’d expect; an asynchronous version of IEnumerable. The language lets you await foreach over these to consume their elements, and yield return to them to produce elements.

async IAsyncEnumerable GetBigResultsAsync()
{
    await foreach (var result in GetResultsAsync())
    {
        if (result > 20) yield return result; 
    }
}