Imported Upstream version 4.0.0~alpha1

Former-commit-id: 806294f5ded97629b74c85c09952f2a74fe182d9

external/referencesource/mscorlib/system/collections/iequalitycomparer.cs

@@ -0,0 +1,28 @@
+// ==++==
+// 
+//   Copyright (c) Microsoft Corporation.  All rights reserved.
+// 
+// ==--==
+/*============================================================
+**
+** Interface:  IEqualityComparer
+**
+** <OWNER>[....]</OWNER>
+** 
+**
+** Purpose: A mechanism to expose a simplified infrastructure for 
+**          Comparing objects in collections.
+**
+** 
+===========================================================*/
+namespace System.Collections {
+    
+    using System;
+    // An IEqualityComparer is a mechanism to consume custom performant comparison infrastructure
+    // that can be consumed by some of the common collections.
+    [System.Runtime.InteropServices.ComVisible(true)]
+    public interface IEqualityComparer {
+        bool Equals(Object x, Object y);
+        int GetHashCode(Object obj);        
+    }
+}