Question

I would like to know if by default is Hashtable passed by reference or by value?

Answer 1

In C#, all parameters are passed by value. But HashTable is a reference type, so the value being passed is a reference to the actual HashTable, if that makes sense.

It thus means the HashTable is not being copied when you pass it as a parameter, but if you try to overwrite the parameter value like so:

private void SomeMethod(HashTable ht)
{
   ...
   ht = new HashTable();
   ...
}

then it will not work, because you’re overwriting the value parameter, not the actual HashTable.