using System;

using System.Collections.Generic;

using System.Linq;

​

namespace ContainsNotDoingWhatIThoughtItWould

{

    public static class Program

    {

        public class MyEquatable : IEquatable<MyEquatable>

        {

            string[] tags;

​

            public MyEquatable(params string[] tags)

            {

                this.tags = tags;

            }

​

            public bool Equals(MyEquatable other)

            {

                if (other == null)

                {

                    return false;

                }

​

                if (this.tags.Count() != other.tags.Count())

                {

                    return false;

                }

                var commonTags = this.tags.Intersect(other.tags);

                return commonTags.Count() == this.tags.Count();

            }

​

            public override int GetHashCode()

            {

                int hash = 17;

                foreach (string element in this.tags.OrderBy(x => x))

                {

                    hash = unchecked(hash * element.GetHashCode());

                }

                return hash;

            }

        }

​

        public static void Main(string[] args)

        {

            // Two objects for the search list

            var a = new MyEquatable("A");

            var ab = new MyEquatable("A", "B");

​

            IEnumerable<MyEquatable> myList = new MyEquatable[] 

            { 

                a, 

                ab 

            };

​

            // This is the MyEquatable that we want to find

            var target = new MyEquatable("A", "B");

​

            // Check that the equality and hashing works

            var isTrue1 = target.GetHashCode() == ab.GetHashCode();

            var isTrue2 = target.Equals(ab);

​

​

            var isFalse1 = target.GetHashCode() == a.GetHashCode();

            var isFalse2 = target.Equals(a);

​

            // Why is this false?

            var whyIsThisFalse = myList.Contains(target);

            Console.WriteLine(whyIsThisFalse);

​

            // If that is false, why is this true?

            var wrappedChildTarget = new List<MyEquatable> { target };

​

            var thisIsTrue = myList.Intersect(wrappedChildTarget).Any();

            Console.WriteLine(thisIsTrue);

        }

    }

}