C# hashcode for array of ints

Question

I have a class that internally is just an array of integers. Once constructed the array never changes. I\'d like to pre-compute a good hashcode so that this class can be ver

Answer 1

You could take a different approach and use a recursive dictionary for each value in your int array. This way you can leave .net to do primitive type hashing.

internal class DictionaryEntry<TKey, TValue>
{
    public Dictionary<TKey, DictionaryEntry<TKey, TValue>> Children { get; private set; }
    public TValue Value { get; private set; }
    public bool HasValue { get; private set; }

    public void SetValue(TValue value)
    {
        Value = value;
        HasValue = true;
    }

    public DictionaryEntry()
    {
        Children = new Dictionary<TKey, DictionaryEntry<TKey, TValue>>();
    }
}

internal class KeyStackDictionary<TKey, TValue>
{
    // Helper dictionary to work with a stack of keys
    // Usage:
    // var dict = new KeyStackDictionary<int, string>();
    // int[] keyStack = new int[] {23, 43, 54};
    // dict.SetValue(keyStack, "foo");
    // string value;
    // if (dict.GetValue(keyStack, out value))
    // {   
    // }

    private DictionaryEntry<TKey, TValue> _dict;

    public KeyStackDictionary()
    {
        _dict = new DictionaryEntry<TKey, TValue>();
    }

    public void SetValue(TKey[] keyStack, TValue value)
    {
        DictionaryEntry<TKey, TValue> dict = _dict;

        for (int i = 0; i < keyStack.Length; i++)
        {
            TKey key = keyStack[i];
            if (dict.Children.ContainsKey(key))
            {
                dict = dict.Children[key];
            }
            else
            {
                var child = new DictionaryEntry<TKey, TValue>();
                dict.Children.Add(key, child);
                dict = child;
            }

            if (i == keyStack.Length - 1)
            {
                dict.SetValue(value);
            }
        }
    }

    // returns false if the value is not found using the key stack
    public bool GetValue(TKey[] keyStack, out TValue value)
    {
        DictionaryEntry<TKey, TValue> dict = _dict;

        for (int i = 0; i < keyStack.Length; i++)
        {
            TKey key = keyStack[i];

            if (dict.Children.ContainsKey(key))
            {
                dict = dict.Children[key];
            }
            else
            {
                break;
            }

            if (i == keyStack.Length - 1 && dict.HasValue)
            {
                value = dict.Value;
                return true;
            }
        }

        value = default(TValue);
        return false;
    }
}