.NET dictionary with two keys and one value

Question

Is there a dictionary available in .NET that could hold 2 keys and one value. Like

Dictionary(Of TKey, Of TKey, TValue)

I have

Answer 1

This is NOT a proper dictionary, but can be used for simple dictionary-like add remove functionalities.

This can be made generic as well, with proper implementation of IComparable in the keys types, and changing the dictionary code accordingly. (Note, default values of keys are not allowed to manage ambiguity!)

internal class KeyValueSet //this dictionary item is tailor made for this example
{
    public string KeyStr { get; set; }
    public int KeyInt { get; set; }
    public int Value { get; set; }

    public KeyValueSet() { }

    public KeyValueSet(string keyStr, int keyInt, int value)
    {
        KeyStr = keyStr;
        KeyInt = keyInt;
        Value = value;
    }
}

public class DoubleKeyDictionary
{
    List _list = new List();

    private void Add(KeyValueSet set)
    {
        if (set == null)
            throw new InvalidOperationException("Cannot add null");
        if (string.IsNullOrEmpty(set.KeyStr) && set.KeyInt == 0)
            throw new InvalidOperationException("Invalid key");
        if (!string.IsNullOrEmpty(set.KeyStr) && _list.Any(l => l.KeyStr.Equals(set.KeyStr))
            || set.KeyInt != 0 && _list.Any(l => l.KeyInt == set.KeyInt))
            throw new InvalidOperationException("Either of keys exists");
        _list.Add(set);
    }

    public void Add(string keyStr, int keyInt, int value)
    {
        Add(new KeyValueSet { KeyInt = keyInt, KeyStr = keyStr, Value = value });
    }

    public void Add(string key, int value)
    {
        Add(new KeyValueSet { KeyInt = 0, KeyStr = key, Value = value });
    }

    public void Add(int key, int value)
    {
        Add(new KeyValueSet { KeyInt = key, KeyStr = string.Empty, Value = value });
    }

    public void Remove(int key)
    {
        if (key == 0)
            throw new InvalidDataException("Key not found");
        var val = _list.First(l => l.KeyInt == key);
        _list.Remove(val);
    }

    public void Remove(string key)
    {
        if (string.IsNullOrEmpty(key))
            throw new InvalidDataException("Key not found");
        var val = _list.First(l => l.KeyStr == key);
        _list.Remove(val);
    }

    public void Remove(KeyValueSet item)
    {
        _list.Remove(item);
    }

    public int this[int index]
    {
        get
        {
            if (index != 0 && _list.Any(l => l.KeyInt == index))
                return _list.First(l => l.KeyInt == index).Value;
            throw new InvalidDataException("Key not found");
        }
        set
        {
            Add(index, value);
        }
    }

    public int this[string key]
    {
        get
        {
            if (!string.IsNullOrEmpty(key) && _list.Any(l => l.KeyStr == key))
                return _list.First(l => l.KeyStr == key).Value;
            throw new InvalidDataException("Key not found");
        }
        set
        {
            Add(key, value);
        }
    }
}

Testing the DoubleKeyDictionary

var dict = new DoubleKeyDictionary();
dict.Add(123, 1);
dict.Add(234, 2);
dict.Add("k1", 3);
dict.Add("k2", 4);            
dict[456] = 5;
dict["k3"] = 6;
dict.Add("k4", 567, 7);
dict.Remove(123);

Console.WriteLine(dict[234]); //2
Console.WriteLine(dict["k2"]); //4
Console.WriteLine(dict[456]); //5
Console.WriteLine(dict[567]); //7
Console.WriteLine(dict["k4"]); //7
Console.WriteLine(dict[123]); //exception