using System;

using System.Threading.Tasks;

using System.Diagnostics;

public class Program

{

    public static void Main()

    {

        AsyncMain().Wait();

    }

    public static async Task AsyncMain()

    {

        int a = 500;

        int b = 10;

        var results = await TimeMeasurer.Start(() => Function(a,b));

        Console.WriteLine("Waited: {0}", results.Duration.TotalSeconds);

        Console.WriteLine("Result: {0}", results.Result);

    }

    public static async Task<int> Function(int a, int b)

    {

        var total = a + b;

        await Task.Delay(total);

        return total;

    }

}

​

    public class TimeMeasurerResult

    {

        protected readonly Task _task;

        private readonly TimeSpan _duration;

        public TimeMeasurerResult(Task task, TimeSpan duration)

        {

            _task = task;

            _duration = duration;

        }

        public Task Task {get { return _task;}}

        public TimeSpan Duration {get {return _duration;}}

    }

​

    public class TimeMeasurerResult<T> : TimeMeasurerResult

    {    

        public TimeMeasurerResult(Task<T> task, TimeSpan duration)

            :base(task, duration)

        {

        }

        public T Result {get { return ((Task<T>)_task).Result;}}

    }

    public static class TimeMeasurer 

    {    

        public static async Task<TimeMeasurerResult<TReturn>> Start<TReturn>(Func<Task<TReturn>> function)

        {

            var stopWatch = Stopwatch.StartNew();

            var task = function();

            await task;

            var took = stopWatch.Elapsed;

            return new TimeMeasurerResult<TReturn>(task, took);

        }

        public static async Task<TimeMeasurerResult> Start(Func<Task> function)

        {

            var stopWatch = Stopwatch.StartNew();

            var task = function();

            await task;

            var took = stopWatch.Elapsed;

            return new TimeMeasurerResult(task, took);

        }    

    }