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

   1 //---------------------------------------------------------------------
   2 // <copyright file="TrailingSpaceComparer.cs" company="Microsoft">
   3 //      Copyright (c) Microsoft Corporation.  All rights reserved.
   4 // </copyright>
   5 //
   6 // @owner Microsoft
   7 // @backupOwner Microsoft
   8 //---------------------------------------------------------------------
   9
  10 using System.Collections.Generic;
  11 namespace System.Data.Common.Utils
  12 {
  13     /// <summary>
  14     /// Comparer that treats two strings as equivalent if they differ only by trailing
  15     /// spaces, e.g. 'A' eq 'A   '. Useful when determining if a set of values is unique
  16     /// even given the possibility of padding (consider SQL Server char and nchar columns)
  17     /// or to lookup values when the set of values is known to honor this uniqueness constraint.
  18     /// </summary>
  19     internal class TrailingSpaceComparer : IEqualityComparer<object>
  20     {
  21         private TrailingSpaceComparer() { }
  22         internal readonly static TrailingSpaceComparer Instance = new TrailingSpaceComparer();
  23         private readonly static IEqualityComparer<object> s_template = EqualityComparer<object>.Default;
  24         bool IEqualityComparer<object>.Equals(object x, object y)
  25         {
  26             string xAsString = x as string;
  27             if (null != xAsString)
  28             {
  29                 string yAsString = y as string;
  30                 if (null != yAsString)
  31                 {
  32                     return TrailingSpaceStringComparer.Instance.Equals(xAsString, yAsString);
  33                 }
  34             }
  35             return s_template.Equals(x, y);
  36         }
  37         int IEqualityComparer<object>.GetHashCode(object obj)
  38         {
  39             string value = obj as string;
  40             if (null != value)
  41             {
  42                 return TrailingSpaceStringComparer.Instance.GetHashCode(value);
  43             }
  44             return s_template.GetHashCode(obj);
  45         }
  46     }
  47
  48     /// <summary>
  49     /// Typed version of TrailingSpaceComparer.
  50     /// </summary>
  51     internal class TrailingSpaceStringComparer : IEqualityComparer<string>
  52     {
  53         internal static readonly TrailingSpaceStringComparer Instance = new TrailingSpaceStringComparer();
  54         private TrailingSpaceStringComparer() { }
  55         public bool Equals(string x, string y)
  56         {
  57             return StringComparer.OrdinalIgnoreCase.Equals(NormalizeString(x), NormalizeString(y));
  58         }
  59         public int GetHashCode(string obj)
  60         {
  61             return StringComparer.OrdinalIgnoreCase.GetHashCode(NormalizeString(obj));
  62         }
  63         internal static string NormalizeString(string value)
  64         {
  65             if (null == value || !value.EndsWith(" ", StringComparison.Ordinal)) { return value; }
  66             else { return value.TrimEnd(' '); }
  67         }
  68     }
  69 }