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This was a question in one of my interview with American Express, and this was how I understand the question:

 that I  In VB.NET, I found there are a lots methods passing object parameter by value. For example,

Private Sub Button3_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button3.Click

It's impossible in vb6.In vb6, the object is always passed by reference.
How come we can pass object byval in .NET?

An object in both VB6 & VB.NET is a Reference Type!

ByVal & ByRef Parameters are independent of Reference & Value Types. All
parameters in VB.NET by default are passed ByVal, you should only pass a
parameter ByRef when you have to, which is when you need to modify the
callers variable.

A Reference Type is an object that exists on the heap. If I have a variable
that is a reference type and assign the variable to another variable. Both
variables will be pointing to the same object on the heap.

Dim x As Person
x = New Person()
Dim y As Person
y = x

Both x & y are the exact same Person object on the heap.

A Value Type does not live on the Heap. If I have a value type variable and
I assign it to another variable, a copy of the value is made.

Dim x As Integer
x = 100
Dim y As Integer
y = x

Although both x & y have the value 100, they are physically different values
as a copy was made.

Now when you pass a variable to a ByVal parameter a copy of the variable is
made. So for a Reference Type a copy of the reference is made, which means
there is still only one object on the heap & two references to that object.
For a Value Type a copy of the value is made.

When you pass a variable to a ByRef parameter a reference to that variable
is made. So for a Reference Type you have a reference to a reference to the
object, for a Value Type you have a reference to the value.

Remember ByVal & ByRef are how parameters are passed. Reference & Value
Types are how quantities are stored.


Posted on Thursday, June 22, 2006 9:34 AM | Back to top


Comments on this post: use byval for object in method signature

# re: use byval for object in method signature
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Hey,

I with you on this post. Did American Express really asked you that? Did you get a job with them?
Left by Cathyline Wordern on Jun 26, 2006 5:35 PM

# re: use byval for object in method signature
Requesting Gravatar...
Look like you are working with VB6.0 right?
the post is great, and good explaination...
Left by Lien Luc on Jun 26, 2006 5:37 PM

# re: use byval for object in method signature
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Great articles...
Left by Tim Hutchinson on Jun 26, 2006 8:47 PM

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