using System;

using System.Collections.Generic;

​

public class Program

{

    public static void Main()

    {

        var item1 = new Test {Test1 = "hello", Test2 = new HashSet<int> { 1, 2, 3 }};

        var item2 = new Test {Test1 = "hello", Test2 = new HashSet<int> { 2, 3, 4 }};

​

        TestItems(item1, item2);

        TestItems(item1, item1);

​

        void TestItems(Test test1, Test test2)

        {

            Console.WriteLine($"Testing {test1} VS. {test2}\n");

            Console.WriteLine($"test1.GetHashCode() = {test1.GetHashCode()}");

            Console.WriteLine($"test2.GetHashCode() = {test2.GetHashCode()}");

            Console.WriteLine($"test1.Equals(test2) = {test1.Equals(test2)}");

​

            var hash = new HashSet<Test>();

​

            Console.WriteLine($"hash.Add(test1) = {hash.Add(test1)}");

            Console.WriteLine($"hash.Add(test2) = {hash.Add(test2)}");

​

            var dict = new Dictionary<Test, string> {{ test1, "" } };

            Console.WriteLine("dict.Add(test1, \"\")");

            Console.WriteLine($"dict.ContainsKey(test2) = {dict.ContainsKey(test2)}\n");

        }

    }

​

    public class Test : IEquatable<Test>

    {

        public string Test1 { get; set; }

        public HashSet<int> Test2 { get; set; }

​

        public bool Equals(Test other)

        {

            Console.WriteLine($"  Equals: {this}");

            if (ReferenceEquals(null, other)) return false;

            if (ReferenceEquals(this, other)) return true;

            if (Test1 != other.Test1) return false;

            if (ReferenceEquals(null, other.Test2)) return false;

            if (ReferenceEquals(Test2, other.Test2)) return true;

            if (Test2.Count != other.Test2.Count) return false;

​

            foreach (var i in Test2)

                if (!other.Test2.Contains(i))

                    return false;

​

            return true;

        }

​

        public override bool Equals(object obj) => Equals(obj as Test);

​

        public override int GetHashCode()

        {

            Console.WriteLine($"  GetHashCode: {this}");

            unchecked

            {

                return ((Test1 != null ? Test1.GetHashCode() : 0) * 397) ^ Test2.GetHashCode();

            }

        }

​

        public override string ToString()

        {

            var test2 = Test2 == null ? null : string.Join(",", Test2);

            return $"{Test1},({test2})";

        }

    }

}