(chocolateyGH-1612) Added extension method and struct

- To allow for correctly generating hash code of objects

src/chocolatey/EnumerableExtensions.cs

@@ -97,5 +97,28 @@ public static IEnumerable<T> distinct_last<T>(this IEnumerable<T> source, IEqual
                 yield return maxElement;
             }
         }
+
+        /// <summary>
+        ///   Generates a unique hash code for a source of objects
+        /// </summary>
+        /// <typeparam name="T">Generic type.</typeparam>
+        /// <param name="source">The source.</param>
+        /// <returns>
+        ///   Integer value representing hash code for input collection.
+        /// </returns>
+        /// <remarks>
+        ///   Taken from here: https://stackoverflow.com/a/30758270/671491
+        /// </remarks>
+        public static int get_sequence_hash_code<T>(this IEnumerable<T> source)
+        {
+            const int seed = 487;
+            const int modifier = 31;
+
+            unchecked
+            {
+                return source.Aggregate(seed, (current, item) =>
+                    (current*modifier) + item.GetHashCode());
+            }
+        }
     }
 }

src/chocolatey/chocolatey.csproj

@@ -122,6 +122,7 @@
     <Compile Include="infrastructure.app\events\HandlePackageResultCompletedMessage.cs" />
     <Compile Include="infrastructure.app\templates\ChocolateyTodoTemplate.cs" />
     <Compile Include="infrastructure.app\utility\ArgumentsUtility.cs" />
+    <Compile Include="infrastructure.app\utility\HashCode.cs" />
     <Compile Include="infrastructure.app\utility\PackageUtility.cs" />
     <Compile Include="infrastructure\logging\AggregateLog.cs" />
     <Compile Include="infrastructure\logging\LogLevelType.cs" />
@@ -368,4 +369,4 @@
   <Target Name="AfterBuild">
   </Target>
   -->
-</Project>
+</Project>

src/chocolatey/infrastructure.app/utility/HashCode.cs

@@ -0,0 +1,75 @@
+// The MIT License (MIT)
+//
+// Copyright (c) Muhammad Rehan Saeed
+//
+// Taken from this blog post: https://rehansaeed.com/gethashcode-made-easy/
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy of
+// this software and associated documentation files (the "Software"), to deal in
+// the Software without restriction, including without limitation the rights to
+// use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
+// the Software, and to permit persons to whom the Software is furnished to do so,
+// subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+// FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+// COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
+// IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+// CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+
+using System.Collections.Generic;
+using System.Linq;
+
+public struct HashCode
+{
+    private readonly int value;
+
+    private HashCode(int value)
+    {
+        this.value = value;
+    }
+
+    public static implicit operator int(HashCode hashCode)
+    {
+        return hashCode.value;
+    }
+
+    public static HashCode Of<T>(T item)
+    {
+        return new HashCode(GetHashCode(item));
+    }
+
+    public HashCode And<T>(T item)
+    {
+        return new HashCode(CombineHashCodes(this.value, GetHashCode(item)));
+    }
+
+    public HashCode AndEach<T>(IEnumerable<T> items)
+    {
+        if (items == null)
+        {
+            return new HashCode(this.value);
+        }
+
+        var hashCode = items.Any() ? items.Select(GetHashCode).Aggregate(CombineHashCodes) : 0;
+        return new HashCode(CombineHashCodes(this.value, hashCode));
+    }
+
+    private static int CombineHashCodes(int h1, int h2)
+    {
+        unchecked
+        {
+            // Code copied from System.Tuple so it must be the best way to combine hash codes or at least a good one.
+            return ((h1 << 5) + h1) ^ h2;
+        }
+    }
+
+    private static int GetHashCode<T>(T item)
+    {
+        return item == null ? 0 : item.GetHashCode();
+    }
+}