using System;

using System.Threading.Tasks;

using System.Runtime.CompilerServices;

public class Program

{

    public static async Task Main()

    {

        var r = await GetMyResult();

        await r;

        Console.WriteLine("Hello World");

    }

    public static async Task<MyResult> GetMyResult()

    {

        await Task.Yield();

        return new MyResult();

    }

}

​

public sealed class MyResult

{

    public async Task WaitForCompletion()

    {

        await Task.Delay(2000);

        Console.WriteLine("Done");

    }

}

​

public static class MyResultEx

{

    public static TaskAwaiter GetAwaiter(this MyResult result) => result.WaitForCompletion().GetAwaiter();

}