How to await all results from an IAsyncEnumerable<>?

Question

I'm tinkering around with the new IAsyncEnumerable<T> stuff in C# 8.0. Let's say I've got some method somewhere that I want to consume:

public IAsyncEnumerable<T> SomeBlackBoxFunctionAsync<T>(...) { ... }

I'm aware that I can use it with the await foreach... syntax. But let's say my consumer needs to have all results from this function before it continues. What's the best syntax to await all results before continuing? In other words, I'd like to be able to do something like:

// but that extension - AllResultsAsync() - doesn't exist :-/
List<T> myList = await SomeBlackBoxFunctionAsync<T>().AllResultsAsync(); 

What's the correct way to do this?

Answer 1

Based on @DmitryBychenko's comment, I wrote an extension to do want I want:

    public static async Task<ICollection<T>> AllResultsAsync<T>(this IAsyncEnumerable<T> asyncEnumerable)
    {
        if (null == asyncEnumerable)
            throw new ArgumentNullException(nameof(asyncEnumerable));  

        var list = new List<T>();
        await foreach (var t in asyncEnumerable)
        {
            list.Add(t);
        }

        return list;
    }

I'm just a little surprised this wasn't shipped natively with C# 8.0...it seems like a pretty obvious need.