example.cs

    class InCompletionOrderQuestion2
    {
        static async Task Main(string[] args)
        {
            await InArrivalOrderFixed.DoWorkAsync();
        }

        public static class InArrivalOrderFixed
        {
            public static async Task DoWorkAsync()
            {
                var numbers = new List<int> { 10, 1, 2, 3, 4, 5, 6, 7, 8, 9 };
                foreach (var task in numbers.Select(x => CreateTask(x)).InCompletionOrder())
                {
                    var delay = await task;
                    Console.WriteLine(delay);
                }
                static async Task<int> CreateTask(int i)
                {
                    await Task.Delay(1000 * i);
                    Console.WriteLine("Number: " + i);
                    return i;
                }
            }
        }
    }