通用的IEqualityComparer< T>和GetHashCode [英] Generic IEqualityComparer<T> and GetHashCode

问题描述

来有些懒惰有关实现大量IEqualityComparers的，鉴于我无法轻松地编辑对象的类实现被比较，我去以下，意味着与鲜明的（）和除（）扩展方法使用。

Being somewhat lazy about implementing lots of IEqualityComparers, and given that I couldn't easily edit class implementations of object being compared, I went with the following, meant to be used with Distinct() and Except() extension methods. :

public class GenericEqualityComparer<T> : IEqualityComparer<T>
{
    Func<T, T, bool> compareFunction;
    Func<T, int> hashFunction;

    public GenericEqualityComparer(Func<T, T, bool> compareFunction, Func<T, int> hashFunction)
    {
        this.compareFunction = compareFunction;
        this.hashFunction = hashFunction;
    }

    public bool Equals(T x, T y)
    {
        return compareFunction(x, y);
    }

    public int GetHashCode(T obj)
    {
        return hashFunction(obj);
    }
}

似乎不错，但实在是给人一种散列函数everytimes有必要吗？
我明白的哈希码是用来放对象桶。不同的水桶，对象不相等，且等于不叫。

Seems nice, but is giving an hash function everytimes REALLY necessary ? I understand that the hashcode is used to put objects in buckets. Different buckets, object are not equal, and equal is not called.

如果GetHashCode返回相同的值，等于被调用。 （来源：为什么是重要的，当equals方法在C＃中被重写重写GetHashCode？）

If GetHashCode returns the same value, equals is called. ( from : Why is it important to override GetHashCode when Equals method is overriden in C#? )

那么，什么可能出错，例如，如果（我听到很多程序员惊恐尖叫），G​​etHashCode返回一个常数，以强制调用平等？

So what could go wrong, if for example (and I hear a lot of programmers screaming in horror), GetHashCode returns a constant, to force the call to Equal ?

推荐答案

不会有事，但在基于散列的表箱，你从约O（1）进行查找时要O（n）性能。你会更好只是存储在一个列表的一切，蛮力搜索这对于实现平等的项目。

Nothing would go wrong, but in hash-table based containers, you're going from approx O(1) to O(n) performance when doing a lookup. You'd be better off simply storing everything in a List and brute force searching it for items that fulfil equality.

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