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//---------------------------------------------------------------------
// <copyright file="TrailingSpaceComparer.cs" company="Microsoft">
// Copyright (c) Microsoft Corporation. All rights reserved.
// </copyright>
//
// @owner Microsoft
// @backupOwner Microsoft
//---------------------------------------------------------------------
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(' '); }
}
}
}
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