Question

I am trying to write a recursive C# function that will operate on generic dictionaries of the form IDictionary<string, T> where T is either another IDictionary<string, T> or a string.

My first failed attempt looked something like this:

public string HandleDict(IDictionary<string, string> dict){
    // handle the leaf-node here
}

public string HandleDict<T>(IDictionary<string, IDictionary<string, T>> dict){
    // loop through children
    foreach(string key in dict.Keys){
        HandleDict(dict[key]);
    }
}

I also tried variants of HandleDict<T>(IDictionary<string, T>) where T : IDictionary<string, T> but that also doesn’t quite work. I know that what I want to do could be achieved through a custom class as the parameter instead of dictionaries, and that my attempts are conceptually flawed (there’s no end to the recursion in the generic function). I would still like to know if there is actually a way to do what I want here using just generic IDictionaries.

Answer 1

The C# type system is not powerful enough to represent the sort of “higher” generic types that you need to do this in the type system proper. Consider Haskell or F# if you need a language with a richer generic type system.

It is possible to do what you want in C# 4 using the ‘dynamic’ feature, but I’d recommend against it. Doing that basically starts up the compiler again at runtime. Rather than resorting to runtime type analysis I’d spend some time revisiting the decision to use dictionaries in the first place. I suspect there are better data structures for your actual task at hand. Describe that task and we’ll see if there are better data structures.