passing object byVal or byref

Hi, and welcome to the forum.

That looks like one of Chip Pearson's example on his web site. Does his explanation along with it not help?

When you pass an argument to a procedure by reference it uses the original value. The variable value is changed in the function.

When you pass an argument by value you pass a copy to the function. The original value is not changed.

Originally Posted by alexba

Hi Richard

but the correct output is

AFTER CALL::Range1: A3 =
AFTER CALL::Range2: A2 = 654

.
Alex

Indeed. And that's what the code gives you. The R1 By Ref argument is modified in the Called Procedure by the A3 Value which is blank. Perhaps it's easier to understand if you comment out the
R1.Value = 321
R2.Value = 654

Then the output is

BEFORE CALL::Range1: A1 = 123
BEFORE CALL::Range2: A2 = 456
AFTER CALL::Range1: A3 =
AFTER CALL::Range2: A2 = 456

i.e R1 has been modified to reflect the A3 vale, whereas although you set R2 to be the A4 value , i.e. Nil, it still carries the original value.

Originally Posted by alexba

Hi Richard

Thank for your quick reply . last question please. hopefully my explanation make sense on the right of the code.

Sub CalledProcedure(ByRef R1 As Range, ByVal R2 As Range)

R1.Value = 321             '         Cell A1.Value=321
R2.Value = 654             '         Cell A2.Value=654

Set R1 = Range("A3")    '   cell A1=Cell A3 but not the value.  so that is why A3 is blank
Set R2 = Range("A4")   '   cell  A2=Cell A4 but not the value.                       A4 is blank
End Sub

so when the code is run. the output is
AFTER CALL::Range1: A3 = because passing object by ref, the object is changed from A1 to A3, but as cell A3 is blank.
AFTER CALL::Range2: A2 = 456 because passing object by val, the object is not changed ,stil A2, but as cell A2 is assigned a new value 654 .


Kind regards

Alex

Hi,

Essentially Yes. But don't confuse cells on the sheet with a VBA variable
You suggest above
AFTER CALL::Range2: A2 = 456 because passing object by val, the object is not changed ,stil A2, but as cell A2 is assigned a new value 654 .

A2 has NOT been assigned a new value of 654. Nowhere in the code is A2 assigned (or in normal parlance has been populated with ) a value. It's the variable R2 that has been assigned the value 654 and that is NOT modified by the Set R2 = Range("A4"). R2 is a 'By Value' variable and Bt Value variables are not modified.

Hi Alex

I was just about to give You the same explanation given to You by Rory over there. ( Post #6 ). So he saved me some time. I can recommend that explanation
Just one last point to be sure you caught.

It may be worth remembering that Passing Objects are a special case of passing ByVal or ByRef.

Most Things:

For most things passing a Variable ByRef means changes done to that in the called routine will be reflected in ( referenced to ) the Original ( ORefiginal ) Variable. I think we all agree there.

For most things passing a variable ByVal means at the Call a full copy is made of the original Variable. Changes done to that Copy Variable in the called routine will be reflected in ( referenced to ) that Copy variable. That Copy variable “dies” at the end of the Called routine. So the original is not affected in any way. I think we all agree there also


For Objects:

These are a special case.

The ByRef case is similar to before.**

The ByVal case is subtly different. Check out again Rory’s “Piece of paper” explanation: For ByVal for an Object you do not make a full copy as in most cases. You copy that piece of paper. So Both the original Paper and the Copy Paper references the Original Object. The “instructions” on the two pieces of paper ( concerning things like where the Values of that Object are stored and what values they have etc.... ) are the same. Reading either piece of paper causes you to do the same thing. So changes done ByVal in the called procedure will still be referenced back to the original Object. Just as they were in the ByRef case. But if you change that Object itself in the ByVal procedure, such as trying to offset it to a different cell, ( different cell = Different Object for a Range object for example ) you will see the change is affected in the Called routine, but not to the Original Object. The Copied piece of paper “dies” at the end of the called procedure. The Object you used in that called procedure dies with it. I am not clear where that Copy Object comes from. Apparantly, according to our explanations, it was not copied from the original. Maybe it is just a local Variable of the type of the original, but with the difference that it does not get it's own unique bit of paper - it gets that copied paper

Alan

P.s. Note I said similar **. At the Call you hand over the original piece of paper ByRef
So for Objects you allways pass a Piece of paper, the original ( ByRef ) or a copy thereof (ByCopVyalue ) . For Most other things you go to a Pigeon Hole where the paper is. That Pigeon Hole being the Original Pigeion Hole ByRef or the temporary built / copied from the original one when ByVal ( This tempory oigein Hole is demolished with all in it at the end of the calls Procedure ) .
Not sure what that small subtle difference means between the Paper and the Pigeion Hole with a paper in it. . I doubt anyone does as it is all sounds like a right load of old bollox anyway ; )

http://excelmatters.com/2016/03/10/b...he-difference/
http://www.mrexcel.com/forum/excel-q...val-byref.html
http://www.mrexcel.com/forum/excel-q...l-byref-3.html

P. P.s.
I made some notes for myself on all this ByRef ByVal stuff
A copy is here:

http://www.excelforum.com/showthread...t=#post4381274
http://www.excelforum.com/showthread...t=#post4381275
http://www.excelforum.com/showthread...t=#post4381420