c# - Nested Dictionary collection in .NET

Question

The .NET Dictionary<TKey, TValue> object allows assignment of key/values like so:

Dictionary<string, string> dict = new Dictionary<string, string>();
dict["1"] = "foo";
dict["2"] = "bar";

but I cannot use a Dictionary like so:

Dictionary<string, string> dict = new Dictionary<string, string>();
dict["F1"]["F2"]["F3"] = "foo";
dict["2"]["X"] = "bar";

Is there a collection in .NET which allows me to nest [], or would I have to create my own?

If I have to create my own, how would I do this?

EDIT:

It would also be useful if I could have implementations which expect unique keys, like so:

dict["F1"]["F2"]["F3"] = "foo";
dict["F1"]["F2"]["F3"] = "bar"; //result is "bar" because "foo" was overridden

and an implementation where a key can be used more than once

dict["F1"]["F2"]["F3"] = "foo";
dict["F1"]["F2"]["F3"] = "bar"; //result can be "foo" and "bar"

Is this possible?

EDIT (as per Jon Skeet's question):

I want to use the structure like so (as a very rough example):

json["data"]["request"]["name"] = "username";
json["data"]["request"]["pass"] = "password";

resolves to

{ data: { request: { name: "username", pass: "password" } } }

and equally there would be an equivalent for XML etc.

Answer 1

Having a requirement for arbitrarily long nesting, I have come up with the following solution, which as far as I can see, doesn't break, according to my test:

public class NestedDictionary<K, V> : Dictionary<K, NestedDictionary<K, V>>
    {
        public V Value { set; get; }

        public new NestedDictionary<K, V> this[K key]
        {
            set { base[key] = value; }

            get
            {
                if (!base.Keys.Contains<K>(key))
                {
                    base[key] = new NestedDictionary<K, V>();
                }
                return base[key];
            }
        }
    }

TEST:

NestedDictionary<string, string> dict = new NestedDictionary<string, string>();
dict["one"].Value = "Nest level 1";
dict["one"]["two"]["three"].Value = "Nest level 3";
dict["FieldA"]["FieldB"].Value = "Hello World";

Console.WriteLine(dict["one"].Value);
Console.WriteLine(dict["one"]["two"]["three"].Value);
Console.WriteLine(dict["FieldA"]["FieldB"].Value);