From 4d264be7134075ab5f01e02fd0f130daa47b07d9 Mon Sep 17 00:00:00 2001
From: Jeff Walker <Jeff@WalkerCodeRanger.com>
Date: Wed, 30 Dec 2020 13:37:38 -0800
Subject: [PATCH] implement IEquatable, fix Equals, improve GetHashCode (issue
 #34)

---
 Semver.Test/SemVersionComparisonTests.cs |  5 +--
 Semver/SemVersion.cs                     | 49 ++++++++++++++----------
 2 files changed, 30 insertions(+), 24 deletions(-)

diff --git a/Semver.Test/SemVersionComparisonTests.cs b/Semver.Test/SemVersionComparisonTests.cs
index 4c63050..71feb28 100644
--- a/Semver.Test/SemVersionComparisonTests.cs
+++ b/Semver.Test/SemVersionComparisonTests.cs
@@ -148,10 +148,9 @@ public void EqualsNullTest()
         public void EqualsNonSemVersionTest()
         {
             var v = new SemVersion(1);
-            // TODO should return false
-            var ex = Assert.Throws<InvalidCastException>(() => v.Equals(new object()));
+            var r = v.Equals(new object());
 
-            Assert.Equal("Unable to cast object of type 'System.Object' to type 'Semver.SemVersion'.", ex.Message);
+            Assert.False(r);
         }
 
         [Theory]
diff --git a/Semver/SemVersion.cs b/Semver/SemVersion.cs
index ce22a07..3247973 100644
--- a/Semver/SemVersion.cs
+++ b/Semver/SemVersion.cs
@@ -17,13 +17,13 @@ namespace Semver
     /// Conforms with v2.0.0 of http://semver.org
     /// </summary>
 #if NETSTANDARD
-    public sealed class SemVersion : IComparable<SemVersion>, IComparable
+    public sealed class SemVersion : IComparable<SemVersion>, IComparable, IEquatable<SemVersion>
 #else
     [Serializable]
     public sealed class SemVersion : IComparable<SemVersion>, IComparable, ISerializable
 #endif
     {
-        private const string InvalidSemVersionStylesMessage = "An invalid SemVersionStyles value was used.";
+        private const string InvalidSemVersionStylesMessage = "An invalid SemVersionStyles value was used";
 
         /// <summary>
         /// This exception is used with the <see cref="SemVersionParser.Parse"/>
@@ -626,22 +626,31 @@ private static int CompareComponent(string a, string b, bool nonemptyIsLower = f
         /// <returns>
         ///   <see langword="true"/> if the specified <see cref="object" /> is equal to this instance, otherwise <see langword="false"/>.
         /// </returns>
-        /// <exception cref="InvalidCastException">The <paramref name="obj"/> is not a <see cref="SemVersion"/>.</exception>
         public override bool Equals(object obj)
         {
-            if (obj is null)
+            return Equals(obj as SemVersion);
+        }
+
+        /// <summary>
+        /// Indicates whether the <see cref="SemVersion"/> is equal to another <see cref="SemVersion"/>.
+        /// </summary>
+        /// <param name="other">An object to compare with this object.</param>
+        /// <returns>
+        ///   <see langword="true"/> if the current object is equal to the <paramref name="other"/> parameter, otherwise <see langword="false"/>.
+        /// </returns>
+        public bool Equals(SemVersion other)
+        {
+            if (other is null)
                 return false;
 
-            if (ReferenceEquals(this, obj))
+            if (ReferenceEquals(this, other))
                 return true;
 
-            var other = (SemVersion)obj;
-
             return Major == other.Major
-                && Minor == other.Minor
-                && Patch == other.Patch
-                && string.Equals(Prerelease, other.Prerelease, StringComparison.Ordinal)
-                && string.Equals(Metadata, other.Metadata, StringComparison.Ordinal);
+                   && Minor == other.Minor
+                   && Patch == other.Patch
+                   && string.Equals(Prerelease, other.Prerelease, StringComparison.Ordinal)
+                   && string.Equals(Metadata, other.Metadata, StringComparison.Ordinal);
         }
 
         /// <summary>
@@ -652,16 +661,14 @@ public override bool Equals(object obj)
         /// </returns>
         public override int GetHashCode()
         {
-            unchecked
-            {
-                // TODO verify this. Some versions start result = 17. Some use 37 instead of 31
-                int result = Major.GetHashCode();
-                result = result * 31 + Minor.GetHashCode();
-                result = result * 31 + Patch.GetHashCode();
-                result = result * 31 + Prerelease.GetHashCode();
-                result = result * 31 + Metadata.GetHashCode();
-                return result;
-            }
+            // FNV based hash combine generated by VS
+            var hashCode = 276583904;
+            hashCode = hashCode * -1521134295 + Major.GetHashCode();
+            hashCode = hashCode * -1521134295 + Minor.GetHashCode();
+            hashCode = hashCode * -1521134295 + Patch.GetHashCode();
+            hashCode = hashCode * -1521134295 + Prerelease.GetHashCode();
+            hashCode = hashCode * -1521134295 + Metadata.GetHashCode();
+            return hashCode;
         }
 
 #if !NETSTANDARD