ByVal and ByRef meaningless for some objects? (vb.net)

[NeuralJack]

I think I know the answer to this , but just want to double check. Using OOP like a good boy should, I pass forms to other forms often. By default vs.net uses a ByVal word instead of byref. Also, I've seen many other vb.net code examples that pass a form to a form or an object around and ByVal seems to work like ByRef in those instances.

 

Am i right? I sure hope i'm not passing a whole copy of the form over when i use ByVal, and I hope i'm just passing a reference to the form i want to pass. ByVal should actually mean that i'm passing a copy to the new form though, according to old C++, am i right?

 

So are ByVal and ByRef pretty meaningless on many objects such as forms, controls, and other classes besides pure data values?

[IceAzul]

  Stack               Heap
--------------      -----------
| string b;  | ---> | "Hello" |
| int a = 9; |      -----------
--------------

<a> is a value type (the value is on the stack) <b> is a reference type (or pointer, somewhat) to an value on the heap. When <a> or <b> is used ByVal a copy of the value on the stack is used as a parameter. When it is used ByRef, a pointer to <a> or <b> is used. So a ByRef pointer to a heap object is a pointer to a pointer, and you can change what the reference points to.

 

For example

Sub Main
   Dim s As String = "Hello" ' s is on the heap
   Dim i As Integer = 10     ' i is on the stack

   Change (s, i)
   Use (s, i)
End Sub

Sub Change (ByRef rs As String, ByRef ri As Integer)
  rs = "World" ' pointer to local s, changing it to point to the "world" on the heap
  ri = 14        ' pointer to local i, changing the value on the stack to 14
End Sub

Sub Use (ByVal vs As String, ByVal vi As Integer)
  Console.WriteLine(vs) ' is a copy of the pointer to the heap
  Console.WriteLine(vi) ' is a copy of the value
End Sub

Edited January 1, 2007 by IceAzul

[NeuralJack]

Ok thanks for the details. I'll stick with ByVal for heap objects.

 

  Stack               Heap
--------------      -----------
| string b;  | ---> | "Hello" |
| int a = 9; |      -----------
--------------

<a> is a value type (the value is on the stack) <b> is a reference type (or pointer, somewhat) to an value on the heap. When <a> or <b> is used ByVal a copy of the value on the stack is used as a parameter. When it is used ByRef, a pointer to <a> or <b> is used. So a ByRef pointer to a heap object is just a pointer to a pointer.