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Excel function that returns a reference to an object

Posted on 2003-11-03
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Last Modified: 2010-05-18
I want to pass an object to a function and have the function return a reference to the object.  I'm new at vb, can this be done?

Type dt
   name As String
   value As Integer
End Type

Sub test()
Dim v As dt, temp As dt
Set v = New dt
v.name = "pear"
set temp = t(v) 'make temp and v point to the same object
temp.name = "orange" ' this should change v.name too
Range("a1").value = v.name 'make sure it worked

End Sub

Function t(ByRef a As dt) As dt
set t = a ' assign the location in memory of a to t
End Function
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Question by:relsloan
12 Comments
 
LVL 16

Expert Comment

by:Richie_Simonetti
Comment Utility
That code really works?
I think you cannot use new to instantiante a type (it is not an object, just a structure of data)
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LVL 16

Expert Comment

by:Richie_Simonetti
Comment Utility
Maybe if you explain a bit in simply words what you need.
What kind of object must returns and what kind of object you will pass...
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LVL 16

Expert Comment

by:Richie_Simonetti
Comment Utility
To this point:


Type dt
   name As String
   value As Integer
End Type

Sub test()
Dim v As dt, temp As dt
v.name = "pear"
...
....
...
0
 

Author Comment

by:relsloan
Comment Utility
My code does not work as I'm new to vb.  I want to pass any object (reading the help, I don't think I can pass a string and return a pointer to a string - can I?).  I thought that declaring a new type was the same as declaring a new type of object.  You can disregard the dt type and make a new object that you can pass to the function and have the function return a pointer to that object.  Just make sure the object contains a string field, and use the pointer that returns from the function to access the object to change the string.  Then print the new string using the old object that you passed to the function.
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LVL 29

Expert Comment

by:leonstryker
Comment Utility
You can pass a variable by reference in which case it is in effect a pointer.

Sub test()
Dim strVal1 as string

strVal1 = "test1"
test2 strVal1

MsgBox strVal1

End Sub

Function test2(ByRef strVal as String) as Boolean
strVal = "test2"
test2 = True
End Funciton

Teh result of the previous code will be a message box with strVal1 = to "test2"
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Author Comment

by:relsloan
Comment Utility
I want to be able to have two variables in sub that refer to the same object (call them a and b).  a should be created in the sub and b should be set to point to object a in the function.  When I return from the function(in the sub), I want to be able to assign something to b, which should, in affect assign the same thing to a since they are both the same object.
0
 
LVL 16

Expert Comment

by:Richie_Simonetti
Comment Utility
if i understood:


dim a as object, c as object

set a = MakeSame(c)

function MakeSame(x as object) as object
dim b as object
'example?
dim xl as excel.application

set b = new excel.application
set MakeSame = b
end function

Why do you need this anyway?
0
 

Author Comment

by:relsloan
Comment Utility
I want to pass an array to a function and have the function return an element.  Then I want to be able to do stuff to that element (so that the array is also updated with those changes), but not know which memeber of the array I am changing.

I figured out that you can only use set to set an object so I made a new class module- dt:
Dim val As String

Property Get value() As String
   value = val
End Property

Property Let value(v As String)
   val = v
End Property

Sub test()
Dim d As dt, temp As dt
Set d = New dt
d.value = "apple"
Set temp = t(d)
temp.value = "pear"
Range("a1").value = temp.value
End Sub

Function t(ByRef a As dt) As dt
Set t = a
End Function
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LVL 16

Expert Comment

by:Richie_Simonetti
Comment Utility
if you will go to work with arrays of elements, i suggest that instead of an array use a collection class.
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