EqualityHelper.cs
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using NCC.Dependency;
using System;
using System.Collections.Generic;
namespace NCC.Common.Helper
{
/// <summary>
/// 相等比较辅助类，用于快速创建<see cref="IEqualityComparer{T}"/>的实例
/// </summary>
/// <example>
/// var equalityComparer1 = EqualityHelper[Person].CreateComparer(p => p.ID);
/// var equalityComparer2 = EqualityHelper[Person].CreateComparer(p => p.Name);
/// var equalityComparer3 = EqualityHelper[Person].CreateComparer(p => p.Birthday.Year);
/// </example>
/// <typeparam name="T"> </typeparam>
[SuppressSniffer]
public static class EqualityHelper<T>
{
/// <summary>
/// 创建指定对比委托<paramref name="keySelector"/>的实例
/// </summary>
public static IEqualityComparer<T> CreateComparer<TV>(Func<T, TV> keySelector)
{
return new CommonEqualityComparer<TV>(keySelector);
}
/// <summary>
/// 创建指定对比委托<paramref name="keySelector"/>与结果二次比较器<paramref name="comparer"/>的实例
/// </summary>
public static IEqualityComparer<T> CreateComparer<TV>(Func<T, TV> keySelector, IEqualityComparer<TV> comparer)
{
return new CommonEqualityComparer<TV>(keySelector, comparer);
}
private class CommonEqualityComparer<TV> : IEqualityComparer<T>
{
private readonly IEqualityComparer<TV> _comparer;
private readonly Func<T, TV> _keySelector;
public CommonEqualityComparer(Func<T, TV> keySelector, IEqualityComparer<TV> comparer)
{
_keySelector = keySelector;
_comparer = comparer;
}
public CommonEqualityComparer(Func<T, TV> keySelector)
: this(keySelector, EqualityComparer<TV>.Default)
{ }
public bool Equals(T x, T y)
{
return _comparer.Equals(_keySelector(x), _keySelector(y));
}
public int GetHashCode(T obj)
{
return _comparer.GetHashCode(_keySelector(obj));
}
}
}
}