How to unbox a C# object to dynamic type

Question

I'm trying to do something like this:

void someMethod(TypeA object) { ... }

void someMethod(TypeB object) { ... }

object getObject()
{
    if (...) return new TypeA();
    else return new TypeB();
}

object obj = getObject();
(obj.GetType()) obj;  // won't compile
someMethod(obj);

Obviously I'm confused here. I know I could make this work by just writing out a conditional statement --

if (obj.GetType() == typeof(TypeA)) obj = (TypeA)obj;
else if (obj.GetType() == typeof(TypeB)) obj = (TypeB)obj;

-- but isn't there some way to do this at runtime?

EDIT I agree it seems like perhaps not the best design choice, so here's the context. The point of the above code is Repository base class for Mongo DB. I want it to be able to handle different kinds of tables. So, someMethod() is actually remove; and TypeA and TypeB are ObjectID and Guid; the code at the bottom is part of a type-agnostic remove method that accepts the ID as a string; and getObject() is a method to parse the ID parameter.

Mantegna

You are conflating a type T with the runtime type information associated with it: typeof(T). They are not the same thing and cannot be substituted for each other. – Samirasamisen

There are likely to be better design choices, but you left the actual goal of the code out of your post. Maybe we could provide you with a better and totally different way of writing the solution to your problem if you let us know what you were trying to accomplish with this code. – Stereoisomer

@Kirk Woll, I know the difference, I just wanted to illustrate what I was trying to do. – Mantegna

@John Fisher, added the context. I gather that would be maybe a question for "Code Review" exchange, but if you have ideas, I'd be happy to open it as a separate question. – Mantegna

Have a look at Massive. You'll find a lot of good ideas there. – Caryncaryo

Answer 1

If you're using .NET 4 and C# 4, you can use dynamic for this:

dynamic obj = GetObject();
SomeMethod(obj);

Otherwise, you'll have to use reflection to find and invoke the right method. Overload resolution (for non-dynamic types) is performed at compile-time.

(Note that unless TypeA and TypeB are structs, you wouldn't be unboxing anyway...)

Dittman

@RobertHarvey: Not given the way the question's written, where it's picking overloads within the same type. – Dittman

I wasn't aware that overload resolution extended to the runtime type of the dynamic object. – Caryncaryo

@RobertHarvey: That's the whole point of dynamic - that effectively pretty much everything is deferred to execution time, using the actual type of the object. – Dittman

@RobertHarvey: About the only thing that doesn't extend to dynamic is extension methods; those are only available at compile time. – Martica