Passing Types around and using them in as Type Parameters

Question

Why can't I do something like this:

var myDictionary = new Dictionary<string, Type>();

// Add data to dictionary

foreach(var kvPair in myDictionary)
{
    var result = SomeMethod<kvPair.Value>(kvPair.Key); // Error
}

So I cannot use the Type that I have in the Dictionary element and use it in the type parameter. Yes I could just send the dictionary to the SomeMethod(KeyValuePair). However I do not have control of how the function is implemented.

Error: The type or namespace name 'kvPair' could not be found (are you missing a using directive or an assembly reference?

I feel like I am missing something pretty foundational and I am not sure what it is.

@JasonP While that's one possible solution, I think it's a stretch to call it a duplicate since generics aren't mentioned in the question at all. — D Stanley, Nov 03 '14 at 19:26
@JasonP I'm with DStanley. You could otherwise infer it as *Why this doesn't work?* Just the explanation of why it doesn't work, which is missing in the suggested duplicate. That's not a duplicate, but related question. — Sriram Sakthivel, Nov 03 '14 at 19:38

D Stanley · Accepted Answer · 2014-11-03T19:26:52.050

I feel like I am missing something pretty foundational and I am not sure what it is.

Yes, you're missing that generic parameters are static, not dynamic. They are not discoverable at run-time. One option in your case is to use reflection to build the generic method call at run-time:

foreach(var kvPair in myDictionary)
{
    // use reflection to create generic MethodInfo object
    MethodInfo mi = typeof(this).GetMethod("SomeMethod");
    MethodInfo mig = mi.MakeGenericMethod(kvPair.Value);

    // call generic method
    Object result = mig.Invoke(this, new object[] {kvPair.Key}); 

    // cast to desired return type.
}

Before going down that road, however, I would take a step back and see if generics are the best design now you know that they aren't late-bound.

Ahh this makes a lot of sense now. Hmmm ... I like the solution, its interesting, but idk if I want to use reflection to accomplish this. I'll Have to do some more thinking about what I am trying to do. Thanks! — Schanckopotamus, Nov 03 '14 at 19:32

Passing Types around and using them in as Type Parameters

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