Parallel.For

GetHashesNonUnique.cs

using System;
using System.Diagnostics;
using System.Linq;
using System.Collections.Generic;
using System.Threading.Tasks;

Console.WriteLine($"***** GetHashCode not Unique with Anonymous Types *****\n");

var etalon = new { CurrentSpeed = 55, SomeBool = true };
Console.WriteLine($"Etalon properties: CurrentSpeed: {etalon.CurrentSpeed}, SomeBool:{etalon.SomeBool}");
var etalonHash = etalon.GetHashCode();

///Here values calculated on my machine.
var calculated = new { CurrentSpeed = 207886160, SomeBool = false };
if (calculated.GetType() != etalon.GetType())
    throw new InvalidOperationException("not same anonymous types");
if (calculated.GetHashCode() == etalonHash && !calculated.Equals(etalon))
{
    Console.WriteLine($"Same type, different Values, but equal hashes!!!:");
    Console.WriteLine($" CurrentSpeed: {calculated.CurrentSpeed}, SomeBool:{calculated.SomeBool}");
    return;
}

var sw = new Stopwatch();
sw.Start();
FindCollision();
Console.WriteLine($" elapsed : {sw.Elapsed}");

void FindCollision()
{
    var getAndCompareHashes = InferFunc(etalon,
        (speed, someBool) =>
    {
        var candidate = new { CurrentSpeed = speed, SomeBool = someBool };
        if (candidate.GetType() != etalon.GetType())
            throw new InvalidOperationException("not same anonymous types");
        if (candidate.Equals(etalon))
        {
            return null;
        }

        var h2 = candidate.GetHashCode();
        if (etalonHash == h2)
        {

            Console.WriteLine($"** {speed}!={etalon.CurrentSpeed}. Equals: {candidate.Equals(etalon)}");
            Console.WriteLine($" elapsed : {sw.Elapsed}");
            return candidate;
        }
        return null;
    });

    Console.WriteLine($"Collision finding. Please wait ~30 sec. depending on your hardware....");
    var found = etalon;
    found = null;
    var mode = 1;
    switch (mode)
    {
        case 0:
            {
                var query = ParallelEnumerable.Range(0, int.MaxValue).AsUnordered()
                    .Select(
                (speedi) =>
                        getAndCompareHashes(speedi, true) ??
                        getAndCompareHashes(speedi, false) ??
                        getAndCompareHashes(-speedi, true) ??
                        getAndCompareHashes(-speedi, false)
                    );
                found = query.Where(v => v != null).Take(1).First();
            }
            break;
        case 1:

            Parallel.For(0, int.MaxValue,
                                  (speedi, pls) =>
                                  {
                                      var found1 =
                                           getAndCompareHashes(speedi, true) ??
                                           getAndCompareHashes(speedi, false) ??
                                           getAndCompareHashes(-speedi, true) ??
                                           getAndCompareHashes(-speedi, false);
                                      if (found1 != null)
                                      {
                                          pls.Stop();
                                          found = found1;
                                      }

                                  });


            break;
    }

    Console.WriteLine($"Same type, different Values, but equal hashes!!:");
    Console.WriteLine($" ------ equal?: {found.Equals(etalon)}.  equal hashes?:{found.GetHashCode() == (etalon.GetHashCode())}");
    Console.WriteLine($"found: CurrentSpeed: {found.CurrentSpeed}, SomeBool:{found.SomeBool}\n");

}

//workaround anonymous types.
Func<int, bool, T> InferFunc<T>(T _, Func<int, bool, T> f)
    => f;

Special for Apress/pro-c-sharp-9-w-.net-core-5#3 🐛.