From daa5a10028e9637b5e55ff103ea31330361407fc Mon Sep 17 00:00:00 2001
From: Paul Louth <p.louth@gmail.com>
Date: Mon, 6 Mar 2017 04:45:24 +0000
Subject: [PATCH] Distinct changes

---
 LanguageExt.Core/DataTypes/List/Lst.Module.cs | 23 ++++++++++++++++---
 LanguageExt.Tests/HashSetTests.cs             |  1 -
 2 files changed, 20 insertions(+), 4 deletions(-)

diff --git a/LanguageExt.Core/DataTypes/List/Lst.Module.cs b/LanguageExt.Core/DataTypes/List/Lst.Module.cs
index b44dc417c..144acfc77 100644
--- a/LanguageExt.Core/DataTypes/List/Lst.Module.cs
+++ b/LanguageExt.Core/DataTypes/List/Lst.Module.cs
@@ -778,6 +778,16 @@ public static IEnumerable<T> distinct<T>(IEnumerable<T> list) =>
         public static IEnumerable<T> distinct<EQ, T>(IEnumerable<T> list) where EQ : struct, Eq<T> =>
             list.Distinct(new EqCompare<T>((x, y) => default(EQ).Equals(x, y)));
 
+        /// <summary>
+        /// Return a new enumerable with all duplicate values removed
+        /// </summary>
+        /// <typeparam name="T">Enumerable item type</typeparam>
+        /// <param name="list">Enumerable</param>
+        /// <returns>A new enumerable with all duplicate values removed</returns>
+        [Pure]
+        public static IEnumerable<T> distinct<T, K>(IEnumerable<T> list, Func<T, K> keySelector, Option<Func<K, K, bool>> compare = default(Option<Func<K, K, bool>>)) =>
+             list.Distinct(new EqCompare<T>((a, b) => compare.IfNone(EqualityComparer<K>.Default.Equals)(keySelector(a), keySelector(b)), a => keySelector(a)?.GetHashCode() ?? 0));
+
         /// <summary>
         /// Returns a new enumerable with the first 'count' items from the enumerable provided
         /// </summary>
@@ -1148,12 +1158,19 @@ public static Tuple<IEnumerable<T>, IEnumerable<T>> span<T>(IEnumerable<T> self,
     class EqCompare<T> : IEqualityComparer<T>
     {
         readonly Func<T, T, bool> compare;
+        readonly Option<Func<T, int>> hashCode = None;
 
         public EqCompare(Func<T, T, bool> compare)
         {
             this.compare = compare;
         }
 
+        public EqCompare(Func<T, T, bool> compare, Func<T, int> hashCode)
+        {
+            this.compare = compare;
+            this.hashCode = hashCode;
+        }
+
         [Pure]
         public bool Equals(T x, T y) =>
             isnull(x) && isnull(y)
@@ -1164,8 +1181,8 @@ public bool Equals(T x, T y) =>
 
         [Pure]
         public int GetHashCode(T obj) =>
-            isnull(obj)
-                ? 0
-                : obj.GetHashCode();
+            hashCode.Match(
+                f => isnull(obj) ? 0 : f(obj),
+                () => 0);
     }
 }
\ No newline at end of file
diff --git a/LanguageExt.Tests/HashSetTests.cs b/LanguageExt.Tests/HashSetTests.cs
index 7765c864e..7c256d379 100644
--- a/LanguageExt.Tests/HashSetTests.cs
+++ b/LanguageExt.Tests/HashSetTests.cs
@@ -1,5 +1,4 @@
 using LanguageExt;
-using LanguageExt.Trans;
 using static LanguageExt.Prelude;
 using static LanguageExt.HashSet;
 using Xunit;