我有一个重写 Equals()方法的结构,编译器抱怨 GetHashCode()没有被重写.
I have a struct that overrides the Equals() method and the compiler complains about GetHashCode() not being overridden.
我的结构:
private struct Key { ... public override int GetHashCode() { return ?; } public int FolderID; public MyEnum SubItemKind; public int SubItemID; }实现 GetHashCode()方法的正确方法是什么?
What is the right way to implement the GetHashCode() method?
a)
return FolderID ^ SubItemKind.GetHashCode() ^ SubItemID;或b)
return FolderID.GetHashCode() ^ SubItemKind.GetHashCode() ^ SubItemID.GetHashCode(); 推荐答案始终是后者.前者是不够的,因为大多数位是0(您的数字很可能很小),而那些零是最高有效位.您会浪费大量的哈希码,从而导致更多的冲突.
Always the latter. The former isn't sufficient because most bits are 0 (your numbers are most likely small), and those zeroes are in the most significant bits. You'd be wasting a lot of the hash code, thus getting a lot more collisions.
另一种常见的处理方式是将每个项目乘以质数并依靠溢出:
Another common way of doing it is to multiply each item by a prime number and relying on overflows:
return unchecked(FolderID.GetHashCode() * 23 * 23 + SubItemKind.GetHashCode() * 23 + SubItemID.GetHashCode());已更新,以根据stakx的注释使用 unchecked 显式支持溢出.
Updated to use unchecked for explicit overflow support as per stakx's comment.
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如何在C#结构中实现GetHashCode()
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