Convert IEnumerable to IAsyncEnumerable It has come to my attention that this is at the top of google search results. Before attempting to use this please read the comments below. This is old, and outdated. The comments contain better solutions. TL&DR: use System.Linq.Async's ToAsyncEnumerable()

AsyncEnumerableExtensions.cs

    public static class AsyncEnumerableExtensions
    {

        public static IAsyncEnumerable<TResult> SelectAsync<T, TResult>(this IEnumerable<T> enumerable,
            Func<T, Task<TResult>> selector)
        {
            return AsyncEnumerable.CreateEnumerable(() =>
            {
                var enumerator = enumerable.GetEnumerator();
                var current = default(TResult);
                return AsyncEnumerable.CreateEnumerator(async c =>
                    {
                        var moveNext = enumerator.MoveNext();
                        current = moveNext
                            ? await selector(enumerator.Current).ConfigureAwait(false)
                            : default(TResult);
                        return moveNext;
                    },
                    () => current,
                    () => enumerator.Dispose());
            });
        }
    }

Consider updating the git description with a "TL&DR: use System.Linq.Async's ToAsyncEnumerable()"

Personally I thought it'd be called AsAsyncEnumerable() and turned to Google after that didn't exist.