A technique to define a dictionary with any kind of keys combination, supporting items with N keys and M keys. All works as long as they implement Equals and GetHashcode, or using IEquitable

MultiKeyDictionary.cs

using System.Runtime.CompilerServices;
using System.Runtime.Serialization;

var specificCombinationDictionary = new MultikeyDictionary<(int,int), string>();
specificCombinationDictionary[(1, 2)] = "3";

var anyKeyDictionary = new MultikeyDictionary<ITuple, string>();
anyKeyDictionary[(1, 2)] = "3";
anyKeyDictionary[("str", DateTime.UtcNow.Date)] = "undefined err";
anyKeyDictionary[(1, 3, 5, "what? a string?!", ("sub?", "Tuple??"))] = "undefined err";


public class MultikeyDictionary<TKey, TValue> : Dictionary<TKey, TValue> where TKey : ITuple {
    public MultikeyDictionary() { }
    public MultikeyDictionary(IDictionary<TKey, TValue> dictionary) : base(dictionary) { }
    public MultikeyDictionary(IDictionary<TKey, TValue> dictionary, IEqualityComparer<TKey>? comparer) : base(dictionary, comparer) { }
    public MultikeyDictionary(IEnumerable<KeyValuePair<TKey, TValue>> collection) : base(collection) { }
    public MultikeyDictionary(IEnumerable<KeyValuePair<TKey, TValue>> collection, IEqualityComparer<TKey>? comparer) : base(collection, comparer) { }
    public MultikeyDictionary(IEqualityComparer<TKey>? comparer) : base(comparer) { }
    public MultikeyDictionary(int capacity) : base(capacity) { }
    public MultikeyDictionary(int capacity, IEqualityComparer<TKey>? comparer) : base(capacity, comparer) { }
    protected MultikeyDictionary(SerializationInfo info, StreamingContext context) : base(info, context) { }
}