1 files changed, 61 insertions, 0 deletions
diff --git a/src/System.Private.CoreLib/shared/System/Collections/CompatibleComparer.cs b/src/System.Private.CoreLib/shared/System/Collections/CompatibleComparer.cs
new file mode 100644
index 000000000..587fd6839
--- /dev/null
+++ b/src/System.Private.CoreLib/shared/System/Collections/CompatibleComparer.cs
@@ -0,0 +1,61 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+#pragma warning disable 618 // obsolete types
+
+namespace System.Collections
+{
+    internal sealed class CompatibleComparer : IEqualityComparer
+    {
+        private readonly IHashCodeProvider _hcp;
+        private readonly IComparer _comparer;
+
+        internal CompatibleComparer(IHashCodeProvider hashCodeProvider, IComparer comparer)
+        {
+            _hcp = hashCodeProvider;
+            _comparer = comparer;
+        }
+
+        internal IHashCodeProvider HashCodeProvider => _hcp;
+
+        internal IComparer Comparer => _comparer;
+
+        public new bool Equals(object a, object b) => Compare(a, b) == 0;
+
+        public int Compare(object a, object b)
+        {
+            if (a == b)
+                return 0;
+            if (a == null)
+                return -1;
+            if (b == null)
+                return 1;
+
+            if (_comparer != null)
+            {
+                return _comparer.Compare(a, b);
+            }
+
+            IComparable ia = a as IComparable;
+            if (ia != null)
+            {
+                return ia.CompareTo(b);
+            }
+
+            throw new ArgumentException(SR.Argument_ImplementIComparable);
+        }
+
+        public int GetHashCode(object obj)
+        {
+            if (obj == null)
+            {
+                throw new ArgumentNullException(nameof(obj));
+            }
+
+            return _hcp != null ?
+                _hcp.GetHashCode(obj) :
+                obj.GetHashCode();
+        }
+    }
+}