Imported Upstream version 4.6.0.125

Former-commit-id: a2155e9bd80020e49e72e86c44da02a8ac0e57a4

mcs/class/referencesource/System.Data.Entity/System/Data/Common/Utils/TrailingSpaceComparer.cs

@@ -0,0 +1,69 @@
+//---------------------------------------------------------------------
+// <copyright file="TrailingSpaceComparer.cs" company="Microsoft">
+//      Copyright (c) Microsoft Corporation.  All rights reserved.
+// </copyright>
+//
+// @owner [....]
+// @backupOwner [....]
+//---------------------------------------------------------------------
+
+using System.Collections.Generic;
+namespace System.Data.Common.Utils
+{
+    /// <summary>
+    /// Comparer that treats two strings as equivalent if they differ only by trailing
+    /// spaces, e.g. 'A' eq 'A   '. Useful when determining if a set of values is unique
+    /// even given the possibility of padding (consider SQL Server char and nchar columns)
+    /// or to lookup values when the set of values is known to honor this uniqueness constraint.
+    /// </summary>
+    internal class TrailingSpaceComparer : IEqualityComparer<object>
+    {
+        private TrailingSpaceComparer() { }
+        internal readonly static TrailingSpaceComparer Instance = new TrailingSpaceComparer();
+        private readonly static IEqualityComparer<object> s_template = EqualityComparer<object>.Default;
+        bool IEqualityComparer<object>.Equals(object x, object y)
+        {
+            string xAsString = x as string;
+            if (null != xAsString)
+            {
+                string yAsString = y as string;
+                if (null != yAsString)
+                {
+                    return TrailingSpaceStringComparer.Instance.Equals(xAsString, yAsString);
+                }
+            }
+            return s_template.Equals(x, y);
+        }
+        int IEqualityComparer<object>.GetHashCode(object obj)
+        {
+            string value = obj as string;
+            if (null != value)
+            {
+                return TrailingSpaceStringComparer.Instance.GetHashCode(value);
+            }
+            return s_template.GetHashCode(obj);
+        }
+    }
+
+    /// <summary>
+    /// Typed version of TrailingSpaceComparer.
+    /// </summary>
+    internal class TrailingSpaceStringComparer : IEqualityComparer<string>
+    {
+        internal static readonly TrailingSpaceStringComparer Instance = new TrailingSpaceStringComparer();
+        private TrailingSpaceStringComparer() { }
+        public bool Equals(string x, string y)
+        {
+            return StringComparer.OrdinalIgnoreCase.Equals(NormalizeString(x), NormalizeString(y));
+        }
+        public int GetHashCode(string obj)
+        {
+            return StringComparer.OrdinalIgnoreCase.GetHashCode(NormalizeString(obj));
+        }
+        internal static string NormalizeString(string value)
+        {
+            if (null == value || !value.EndsWith(" ", StringComparison.Ordinal)) { return value; }
+            else { return value.TrimEnd(' '); }
+        }
+    }
+}