using System;

using System.Collections.Generic;

using System.Linq;

​

namespace asynktest

{

    public class Bob

    {

        public int ID { get; set; }

        public int Value { get; set; }

​

        public override string ToString()

        {

            return $"{ID}-{Value}";

        }

    }

​

    class Program

    {

        static void Main(string[] args)

        {

            var bobs = new List<Bob> { new Bob { ID = 1, Value = 1 }, new Bob { ID = 2, Value = 2 } };

​

            var groupedBobs = bobs.GroupBy(z => z.ID);

​

            Console.ReadLine();

            // What does this output?

            Console.WriteLine(string.Join(",", groupedBobs.First()));

​

            Console.WriteLine(CalculateHash(groupedBobs));

​

            // What does this output?

            Console.WriteLine(string.Join(",", groupedBobs.First()));

        }

​

        private static bool CalculateHash(IEnumerable<IGrouping<int, Bob>> groupedBobs)

        {

            foreach (var entry in groupedBobs)

            {

                // Don't ask why I am doing this...

                entry.First().ID = 5;

            }

​

            return true;

        }

    }

}