using System;

using System.Linq;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        var std = new HashSet<int[]>(new[] { new[] { 1, 2 }, new[] { 2, 2}});

        std.ExceptWith(new[] { new[] { 2, 2}});

        std.Dump();

​

​

        var custom = new HashSet<int[]>(new[] { new[] { 1, 2 }, new[] { 2, 2 } }, new ROCollectionComparer<int>());

        custom.ExceptWith(new[] { new[] { 2, 2 }});

        custom.ExceptWith(new[] { new int[] { }});

        custom.Dump();          

    }

​

    class ROCollectionComparer<T> : IEqualityComparer<IReadOnlyCollection<T>>

    {

        private readonly IEqualityComparer<T> elementComparer;

​

        public ROCollectionComparer() : this(EqualityComparer<T>.Default) {}

        public ROCollectionComparer(IEqualityComparer<T> elementComparer) {

            this.elementComparer = elementComparer;

        }

​

        public bool Equals(IReadOnlyCollection<T> x, IReadOnlyCollection<T> y)

        {

            if(x== null && y == null) return true;

            if(x == null || y == null) return false;

            if(object.ReferenceEquals(x, y)) return true;

​

            return x.Count == y.Count && 

                x.SequenceEqual(y, elementComparer);

        }

​

        public int GetHashCode(IReadOnlyCollection<T> obj)

        {       

            // simplistic implementation - but should OK-ish when just looking for equality

            return Tuple.Create(obj.Count, obj.Count == 0 ? 0 : elementComparer.GetHashCode(obj.First())).GetHashCode();

        }

    }

}