Question

I’m aware that questions like this have been asked before and I doubt it’s possible, but I just wanted to make 100% sure that it isn’t.

In VB.net or C# (either language, it doesn’t matter), I want to cast a variable to a type represented by another Type variable. Here’s an example of the kind of code that would be needed in C#:

Object castMe = new Foo();
Type castTo = typeof(Foo);
Foo beenCast = (castTo.GetRepresentedType())castMe;
beenCast.MethodInFoo();

… or in VB, something like:

Dim castMe As Object = New Foo()
Dim castTo As Type = GetType(Foo)
Dim beenCast As Foo = CType(castMe, castTo.GetRepresentedType())
beenCast.MethodInFoo()

The big problem is obviously specifying a method which will return a Type at runtime for the cast type argument, rather than an actual compile-time type (ie. CType(castMe, Foo)). I don’t quite understand why you can’t do this, though… sure, runtime cast errors may result, but you can also get them when you DO specify a compile-time type. If castMe is not an instance of Foo, then even CType(castMe, Foo) will still throw an InvalidCastException.

Answer 1

If you do know to which type you want to cast you will have to end up with something like this:

public static T Cast<T>(object o) {
  return (T)o;
}

T is now your type argument.

If you don’t know what the type is that you cast to, the compiler can’t know either. That’s a statically typed language for you. If you don’t like such things you may want to have a wander through e.g. ruby.

In cases like that, usual responses are abstactions via base classes or interfaces – extract common behaviour into properties, events and methods that can be used in a statically typed language, even though you don’t know the specific type in a given situation.