Recursive By reference passing of hashtable value in C#

Question

Basically, I'm trying to graft a hashtable to to another, and in any other language, I can get it to work...C#, not so much. If anyone could give me some insight on how I should be doing this, I'd appreciate it. This is what I have so far (which doesn't work - it throws an error saying that I can only pass an lvalue by reference - I understand the problem, just not how to solve it).
private void GraftTables(ref Hashtable mainHash, Hashtable branch)
try
foreach (object key in branch.Keys)
if ( !mainHash.ContainsKey(key) )
//graft
mainHash.Add(key, branch[key]);
else
GraftTables(ref (Hashtable) mainHash[key], (Hashtable)branch[key]);
catch (Exception ex)
throw ex;
Thanks for any help,
Chuck Charbeneau
Lear Corporation
[email protected]

Answer 1

If you are trying to do what Ricky described, I don't think you need to use the ref keyword in the first place. I think your method could just be:
private void GraftTables(Hashtable mainHash, Hashtable branch)
The key point here is that mainHash is essentially a pointer to a Hashtable object, so you end up pointing to and manipulating the same object inside your function whether you pass it by value or by reference. The only difference in passing it as a reference is that you can modify the pointer itself, for example:
private void f1(Hashtable h){  h.Add("A", 1);  h = new Hashtable();  h.Add("A", 2);}
private void f2(ref Hashtable h){  h.Add("A", 1);  h = new Hashtable();  h.Add("A", 2);}
If I call:
Hashtable h = new Hashtable();f1(h);object x = h["A"];
I will get x==1, but if I call:
Hashtable h = new Hashtable();f2(ref h);object x = h["A"];
I will get x==2.