Passing properties ByRef

[Martin Rydman]

Hi Gurus!

Here I was, thinking I knew pretty much the ins and outs of VB, but nooo...Can
somebody explain this:

Private Sub Form_Load()
Dim x As New Class1

Dim p As Integer

myset x.x
myset p
End Sub

Sub myset(ByRef y)
y = 5
End Sub

Class1 contains a simple Public x as Integer. When running this code, p is
being changed by the call to myset, but x.x is not. Why?

TIA
/Martin

[Mattias Sjögren]

>Class1 contains a simple Public x as Integer. When running this code, p is
>being changed by the call to myset, but x.x is not. Why?

Hej Martin,

When you add a Public member variable of a class, what really happens
is that VB creates Public Get and Let methods for you (check the
generated interface on a public class in OLE View). So you could look
at it like this:

' --- Class1 ---

Private m_x As Integer

Public Property Get x() As Integer
x = m_x
End Property

Public Property Let x(new_x As Integer)
m_x = new_x
End property

And this property will of course return a copy of the internal value.
It is this copy that will be changed inside myset() and then thrown
away.


Mattias

__________________________________________________
Mattias Sjögren (MCP) - mattiass @ hem.passagen.se
VB+ http://hem.spray.se/mattias.sjogren/
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[Martin Rydman]

Hej själv, Mattias, och tack!

Just to get this clear in my head. Passing ByRef is *not* an assignment,
just passing a reference intead of a copy. Thus, Property Let is *not* called
(which was obvious once I run it through the debugger). Got it now...

/Martin