问题比较项目实施IComparable的 [英] Problem comparing items implementing IComparable

问题描述

我工作的地方特定选择找到分项的扩展方法。下面的代码

I am working on a extension method where it finds the min item by specific selector. Below the code

    public static T MinBy<T, K>(this IEnumerable<T> src, Func<T, K> selector) where K : struct, IComparable, IConvertible
    {
        var min = default(K);
        T minItem = default(T);
        foreach (var item in src)
        {
            var current = selector(item);
            if (current < min)
            {
                min = current;
                minItem = item;
            }
        }

        return minItem;

    }

这使误差错误操作 <'不能应用于类型的操作数'K'和'K'。但我有指定通用约束K在 struct和IComparable的。我相信所有的数字数据类型可以是满意。

It gives error Error Operator '<' cannot be applied to operands of type 'K' and 'K'. But i have specified the generic constraint K should be Struct and IComparable. I believe all the numeric data type can be satisfied with this.

那么怎么来的，这是一个无效的操作？

Then how come this is a invalid operation.?

推荐答案

IComparable的不会（也不能）说，关于运营商什么。您应该使用：

IComparable doesn't (and can't) say anything about operators. You should be using:

if (current.CompareTo(min) < 0)

运营商是静态的，只有永远的重载的而不是覆盖的。可以不需要接口内操作员，以及一个方法的存在不会奇迹般地改变操作者将执行的操作。 （例如，覆盖等于并不会改变 == 的行为。）

Operators are static, and only ever overloaded rather than overridden. You can't require operators within interfaces, and the presence of a method doesn't magically change what an operator will do. (For example, overriding Equals does not change how == behaves.)

您还应该注意到，作为您的约束只有非泛型 IComparable的界面会谈，你会在每一个操作进行拳击。我建议你​​改变约束 IComparable的< K> 来代替。 （或者删除约束，只是使用的Comparer< K> .DEFAULT 如马克的建议）

You should also note that as your constraint only talks about the nongeneric IComparable interface, you're going to be boxing at every operation. I would suggest you change the constraint to IComparable<K> instead. (Or drop the constraint and just use Comparer<K>.Default as Marc suggested.)

其他的一些评论关于你的方法：

Some other comments about your method:

• 如果所有关键值比默认值多为 K （如：K = int和所有按键均为正），那么你不会找到一个项目


• 您可能希望它接受一个特定的 IComparare< K> （但只有当你放弃可比约束）


• 有没有真正需要约束 K 来的值​​类型。如果我想用字典顺序最早的名字吗？


• 如果没有的元素，它会返回 T ;以配合LINQ的其余部分，我建议抛出出现InvalidOperationException


• 我会建议使用 TSource 和 TKEY的作为类型参数与LINQ更一致

• If all of the key values are more than the default value for K (e.g. K=int and all the keys are positive) then you won't find an item
• You may wish to have an overload which accepts a particular IComparare<K> (but only if you drop the comparable constraint)
• There's no real need to constrain K to a value type. What if I wanted to find the person with the lexicographically earliest name?
• If there are no elements, it will return the default value for T; to fit in with the rest of LINQ I would suggest throwing InvalidOperationException
• I would suggest using TSource and TKey as the type parameters to be more consistent with LINQ

您可能想要看的 MoreLINQ MinBy实施的作为替代。 （纵观一遍，我不知道这是一个好主意，我们需要比较器非空;它或许应该使用默认的比较同样的方式正常LINQ确实，如果比较器为null。）

You may want to look at the MoreLINQ MinBy implementation as an alternative. (Looking over that again, I'm not sure it's a good idea for us to require that comparer is non-null; it should probably use the default comparer in the same way as normal LINQ does if the comparer is null.)

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