问题
I have a struct that overrides the Equals() method and the compiler complains about GetHashCode() not being overridden.
My struct:
private struct Key
{
...
public override int GetHashCode()
{
return ?;
}
public int FolderID;
public MyEnum SubItemKind;
public int SubItemID;
}
What is the right way to implement the GetHashCode() method?
a)
return FolderID ^ SubItemKind.GetHashCode() ^ SubItemID;
or b)
return FolderID.GetHashCode() ^ SubItemKind.GetHashCode() ^ SubItemID.GetHashCode();
回答1:
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.
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());
Edit: Updated to use unchecked for explicit overflow support as per stakx's comment.
来源：https://stackoverflow.com/questions/32502181/how-to-implement-gethashcode-in-a-c-sharp-struct