Umbraco-CMS/src/Umbraco.Core/HashCodeHelper.cs

using System.Collections.Generic;

namespace Umbraco.Core
{
    /// <summary>
    /// Borrowed from http://stackoverflow.com/a/2575444/694494
    /// </summary>
    internal static class HashCodeHelper
    {
        public static int GetHashCode<T1, T2>(T1 arg1, T2 arg2)
        {
            unchecked
            {
                return 31 * arg1.GetHashCode() + arg2.GetHashCode();
            }
        }

        public static int GetHashCode<T1, T2, T3>(T1 arg1, T2 arg2, T3 arg3)
        {
            unchecked
            {
                int hash = arg1.GetHashCode();
                hash = 31 * hash + arg2.GetHashCode();
                return 31 * hash + arg3.GetHashCode();
            }
        }

        public static int GetHashCode<T1, T2, T3, T4>(T1 arg1, T2 arg2, T3 arg3,
            T4 arg4)
        {
            unchecked
            {
                int hash = arg1.GetHashCode();
                hash = 31 * hash + arg2.GetHashCode();
                hash = 31 * hash + arg3.GetHashCode();
                return 31 * hash + arg4.GetHashCode();
            }
        }

        public static int GetHashCode<T>(T[] list)
        {
            unchecked
            {
                int hash = 0;
                foreach (var item in list)
                {
                    if (item == null) continue;
                    hash = 31 * hash + item.GetHashCode();
                }
                return hash;
            }
        }

        public static int GetHashCode<T>(IEnumerable<T> list)
        {
            unchecked
            {
                int hash = 0;
                foreach (var item in list)
                {
                    if (item == null) continue;
                    hash = 31 * hash + item.GetHashCode();
                }
                return hash;
            }
        }

        /// <summary>
        /// Gets a hashcode for a collection for that the order of items
        /// does not matter.
        /// So {1, 2, 3} and {3, 2, 1} will get same hash code.
        /// </summary>
        public static int GetHashCodeForOrderNoMatterCollection<T>(
            IEnumerable<T> list)
        {
            unchecked
            {
                int hash = 0;
                int count = 0;
                foreach (var item in list)
                {
                    if (item == null) continue;
                    hash += item.GetHashCode();
                    count++;
                }
                return 31 * hash + count.GetHashCode();
            }
        }

        /// <summary>
        /// Alternative way to get a hashcode is to use a fluent
        /// interface like this:<br />
        /// return 0.CombineHashCode(field1).CombineHashCode(field2).
        ///     CombineHashCode(field3);
        /// </summary>
        public static int CombineHashCode<T>(this int hashCode, T arg)
        {
            unchecked
            {
                return 31 * hashCode + arg.GetHashCode();
            }
        }
    }
}