Making DLL calls with output parameters in Classic ASP [duplicate] - vbscript

Question

In Classic ASP, I have an object, call it bob. This then has a property called name, with let and get methods.
I have a function as follows:
sub append(byref a, b)
a = a & b
end sub
This is simply to make it quicker to add text to a variable. I also have the same for prepend, just it is a = b & a. I know it would be simple to say bob.name = bob.name & "andy", but I tried using the above functions and neither of them work.
The way I am calling it is append bob.name, "andy". Can anyone see what is wrong with this?

Answer 1

Unfortunately this is a feature of VBScript. It is documented in http://msdn.microsoft.com/en-us/library/ee478101(v=vs.84).aspx under "Argument in a class". The alternative is to use a function. Here is an example illustrating the difference. You can run this from the command line using "cscript filename.vbs.
sub append (a, b)
a = a & b
end sub
function Appendix(a, b)
Appendix = a & b
end function
class ClsAA
dim m_b
dim m_a
end class
dim x(20)
a = "alpha"
b = "beta"
wscript.echo "variable works in both cases"
append a, b
wscript.echo "sub " & a
a = appendix(a, b)
wscript.echo "function " & a
x(10) = "delta"
wscript.echo "array works in both cases"
append x(10), b
wscript.echo "sub " & x(10)
x(10) = appendix( x(10), b)
wscript.echo "function " & x(10)
set objAA = new ClsAA
objAA.m_a = "gamma"
wscript.echo "Member only works in a function"
append objAA.m_a, b
wscript.echo "sub " & objAA.m_a
objAA.m_a = appendix(objAA.m_a, b)
wscript.echo "function " & objAA.m_a

Answer 2

Have you tried using with the keyword CALL:
call append (bob.name, "andy")
Classic ASP is fickel about ByRef and ByVal. By default it uses ByRef -- no reason to specify that. If you call a function with parenthesis (without the call), it will pass the variables as ByVal.
Alternatively, you could accomplish the same with:
function append(byref a, b)
append = a & b
end sub
bob.name = append(bob.name, "andy");
Good luck.

Answer 3

As this other answer correctly states, you are facing limitation of the language itself.
The only other option to achieve what you are after as far as I can see it, is to add such sub routine to the class itself:
Public Sub Append(propName, strValue)
Dim curValue, newValue
curValue = Eval("Me." & propName)
newValue = curValue & strValue
Execute("Me." & propName & " = """ & Replace(newValue, """", """""") & """")
End Sub
Then to use it:
bob.Append "name", "andy"
Less elegant, but working.