1 //---------------------------------------------------------------------
2 // <copyright file="TrailingSpaceComparer.cs" company="Microsoft">
3 // Copyright (c) Microsoft Corporation. All rights reserved.
8 //---------------------------------------------------------------------
10 using System.Collections.Generic;
11 namespace System.Data.Common.Utils
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.
19 internal class TrailingSpaceComparer : IEqualityComparer<object>
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)
26 string xAsString = x as string;
27 if (null != xAsString)
29 string yAsString = y as string;
30 if (null != yAsString)
32 return TrailingSpaceStringComparer.Instance.Equals(xAsString, yAsString);
35 return s_template.Equals(x, y);
37 int IEqualityComparer<object>.GetHashCode(object obj)
39 string value = obj as string;
42 return TrailingSpaceStringComparer.Instance.GetHashCode(value);
44 return s_template.GetHashCode(obj);
49 /// Typed version of TrailingSpaceComparer.
51 internal class TrailingSpaceStringComparer : IEqualityComparer<string>
53 internal static readonly TrailingSpaceStringComparer Instance = new TrailingSpaceStringComparer();
54 private TrailingSpaceStringComparer() { }
55 public bool Equals(string x, string y)
57 return StringComparer.OrdinalIgnoreCase.Equals(NormalizeString(x), NormalizeString(y));
59 public int GetHashCode(string obj)
61 return StringComparer.OrdinalIgnoreCase.GetHashCode(NormalizeString(obj));
63 internal static string NormalizeString(string value)
65 if (null == value || !value.EndsWith(" ", StringComparison.Ordinal)) { return value; }
66 else { return value.TrimEnd(' '); }