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c#performancehashhashcode

What is the fastest way to get a hash of a collection

I am trying to make an extension method in C# that takes in a collection of objects and can make a hash from it. The problem is I haven't been able to figure out a fast way of doing it. I am trying to have it be done in O(1) time but I haven't found any useful information out there. This is what I currently have but it is slow and doesn't really work (its just an example):

public static int GetCollectionHash(this IEnumerable collection)
{
    HashCode hash = new();
    foreach (var o in collection)
    {
        hash.Add(o);
    }
    return hash.ToHashCode();
}
Solution

  • the only way to do what you want is to create your own collection and overriding the add/remove/etc method and update a private variable that contain the hash when they are called

    at that point, just read that new variable