Problem with string as reference parameter when method takes Object C# [duplicate]

Question

Possible Duplicate:
C# : Why doesn't 'ref' and 'out' support polymorphism?

I can't seem to understand why the following does not work in C#:

public static void Swap(ref Object a, ref Object b) {
    Object t = b;
    b = a;
    a = t;
}

//Calls
String fname = "Ford";
Strinf lname = "James";
Swap(ref lname, ref fname);

Is this because String already references to a char array, its immutable?

Answer 1

This is a duplicate of

Why doesn't 'ref' and 'out' support polymorphism?

See that answer for why it doesn't work.

To make it work, you could make a generic method:

public static void Swap<T>(ref T a, ref T b) 
{
    T t = b;     
    b = a;     
    a = t; 
}

And now all the types check out.