What is the best way to implement this composite GetHashCode()

Question

I have a simple class:

public class TileName {
    int Zoom, X, Y;

    public override bool Equals (object obj)
    {
        var o = obj as TileName;
              


        

Answer 1

Neither of the implementations in your question are ideal. For example, they'll return exactly the same hash for { Zoom=1, X=2, Y=3 }, { Zoom=2, X=3, Y=1 }, { Zoom=3, X=1, Y=2 } etc etc.

I usually use something like this:

public override int GetHashCode()
{
    // 269 and 47 are primes
    int hash = 269;
    hash = (hash * 47) + Zoom.GetHashCode();
    hash = (hash * 47) + X.GetHashCode();
    hash = (hash * 47) + Y.GetHashCode();
    return hash;
}

(From memory, I think the C# compiler uses something similar when it generates the GetHashCode methods for anonymous types.)