c# - 使用扩展方法使代码可重用

Question

我试图创建这样的扩展方法：

using System;
using System.Collections.Generic;
using System.Linq;

namespace CommonLibs.CommonClasses.Extensions
{
    public static class EnumerableExt
    {
        public static IEnumerable<T> DistinctBy<T>(this IEnumerable<T> collection, Func<T, object> keyGroup)
        {
            return from x in collection group x by keyGroup into grp select grp.First();
        }
    }
}

但如果我想这样使用它：

public class PricingCoefficient
{
    public int Id { get; set; }
    public double FootageFrom { get; set; }
    public double? FootageTo { get; set; }
    public decimal? Coefficient { get; set; }
}

pricingCoefficients.DistinctBy(x => new { x.Coefficient, x.FootageFrom, x.FootageTo });

它给了我错误：

错误 30 类型“AnonymousType#1”不能用作泛型类型或方法“CommonLibs.CommonClasses.EnumerableExtensions.DistinctBy(System.Collections.Generic.IEnumerable, System.Func)”中的类型参数“TKey”。没有从“AnonymousType#1”到“System.IEquatable”的隐式引用转换。

知道如何使它成为扩展方法吗？

谢谢

Answer 1

您需要另一种类型T2，一个类似的键选择器Func<T, T2> keyGroup并将其称为keyGroup(x)

public static IEnumerable<T> DistinctBy2<T,T2>(this IEnumerable<T> collection, Func<T, T2> keyGroup)
{
    return from x in collection group x by keyGroup(x) into grp select grp.First();
}

Answer 2

尝试这个：

public static IEnumerable<T> DistinctBy<T>(this IEnumerable<T> collection, 
                                           Func<T, object> keyGroup) {
    return from x in collection group x by keyGroup(x) into grp select grp.First();
}

注意：我无法重现您的问题，使用(keyGroup without(x)不会引发任何异常，产生. DistinctBy