From 85f6486238962859455a38a27ffc7a0e1fe5d051 Mon Sep 17 00:00:00 2001
From: David Hall <dahall68@gmail.com>
Date: Wed, 17 Jan 2018 12:27:24 -0700
Subject: [PATCH] Added EnumerableEqualityComparer to provide equality
 comparisons and full hashes of lists.

---
 Core/Collections/EnumerableEqualityComparer.cs | 51 ++++++++++++++++++++++++++
 1 file changed, 51 insertions(+)
 create mode 100644 Core/Collections/EnumerableEqualityComparer.cs

diff --git a/Core/Collections/EnumerableEqualityComparer.cs b/Core/Collections/EnumerableEqualityComparer.cs
new file mode 100644
index 00000000..1d49b156
--- /dev/null
+++ b/Core/Collections/EnumerableEqualityComparer.cs
@@ -0,0 +1,51 @@
+using System.Collections.Generic;
+
+namespace Vanara.Collections
+{
+	/// <summary>
+	/// Checks the linear equality of two enumerated lists. For lists to be equal, they must have the same number of elements and each index must hold the same value in
+	/// each list.
+	/// </summary>
+	/// <typeparam name="T">The element type in the list.</typeparam>
+	public sealed class EnumerableEqualityComparer<T> : IEqualityComparer<IEnumerable<T>>
+	{
+		private static readonly EqualityComparer<T> elementComparer = EqualityComparer<T>.Default;
+
+		/// <summary>Determines whether the specified lists are equal.</summary>
+		/// <param name="first">The first list of type T to compare.</param>
+		/// <param name="second">The second list of type T to compare.</param>
+		/// <returns></returns>
+		public bool Equals(IEnumerable<T> first, IEnumerable<T> second)
+		{
+			if (ReferenceEquals(first, second))
+				return true;
+			if (first == null || second == null)
+				return false;
+			var e1 = first.GetEnumerator();
+			var e2 = second.GetEnumerator();
+			bool move1 = false, move2 = false;
+			while ((move1 = e1.MoveNext()) && (move2 = e1.MoveNext()))
+			{
+				if (!elementComparer.Equals(e1.Current, e2.Current))
+					return false;
+			}
+			return move1 == move2;
+		}
+
+		/// <summary>Returns a hash code for the specified object.</summary>
+		/// <param name="list">The Object for which a hash code is to be returned.</param>
+		/// <returns>A hash code for the specified object.</returns>
+		public int GetHashCode(IEnumerable<T> list)
+		{
+			unchecked
+			{
+				if (list == null)
+					return 0;
+				var hash = 17;
+				foreach (T element in list)
+					hash = hash * 31 + elementComparer.GetHashCode(element);
+				return hash;
+			}
+		}
+	}
+}
\ No newline at end of file