VBScript conditional short-circuiting workaround - asp-classic

Question

I have a large classic ASP app that I have to maintain, and I repeatedly find myself thwarted by the lack of short-circuit evaluation capability. E.g., VBScript won't let you get away with:
if not isNull(Rs("myField")) and Rs("myField") <> 0 then
...
...because if Rs("myField") is null, you get an error in the second condition, comparing null to 0. So I'll typically end up doing this instead:
dim myField
if isNull(Rs("myField")) then
myField = 0
else
myField = Rs("myField")
end if
if myField <> 0 then
...
Obviously, the verboseness is pretty appalling. Looking around this large code base, the best workaround I've found is to use a function the original programmer wrote, called TernaryOp, which basically grafts in ternary operator-like functionality, but I'm still stuck using a temporary variable that would not be necessary in a more full-featured language. Is there a better way? Some super-secret way that short-circuiting really does exist in VBScript?

Answer 1

Nested IFs (only slightly less verbose):
if not isNull(Rs("myField")) Then
if Rs("myField") <> 0 then

Answer 2

Maybe not the best way, but it certainly works... Also, if you are in vb6 or .net, you can have different methods that cast to proper type too.
if cint( getVal( rs("blah"), "" ) )<> 0 then
'do something
end if
function getVal( v, replacementVal )
if v is nothing then
getVal = replacementVal
else
getVal = v
end if
end function

Answer 3

I always used Select Case statements to short circuit logic in VB. Something like..
Select Case True
Case isNull(Rs("myField"))
myField = 0
Case (Rs("myField") <> 0)
myField = Rs("myField")
Case Else
myField = -1
End Select
My syntax may be off, been a while. If the first case pops, everything else is ignored.

Answer 4

If you write it as two inline IF statements, you can achieve short-circuiting:
if not isNull(Rs("myField")) then if Rs("myField") <> 0 then ...
But your then action must appear on the same line as well. If you need multiple statements after then, you can separate them with : or move your code to a subroutine that you can call. For example:
if not isNull(Rs("myField")) then if Rs("myField") <> 0 then x = 1 : y = 2
Or
if not isNull(Rs("myField")) then if Rs("myField") <> 0 then DoSomething(Rs("myField"))

Answer 5

Or perhaps I got the wrong end of the question. Did you mean something like iIf() in VB? This works for me:
myField = returnIf(isNothing(rs("myField")), 0, rs("myField"))
where returnIf() is a function like so:
function returnIf(uExpression, uTrue, uFalse)
if (uExpression = true) then returnIf = uTrue else returnIf = uFalse : end if
end function

Answer 6

Yeah it's not the best solution but what we use is something like this
function ReplaceNull(s)
if IsNull(s) or s = "" then
ReplaceNull = " "
else
ReplaceNull = s
end if
end function

Answer 7

Would that there were, my friend -- TernaryOp is your only hope.

Answer 8

Two options come to mind:
1) use len() or lenb() to discover if there is any data in the variable:
if not lenb(rs("myField"))=0 then...
2) use a function that returns a boolean:
if not isNothing(rs("myField")) then...
where isNothing() is a function like so:
function isNothing(vInput)
isNothing = false : vInput = trim(vInput)
if vartype(vInput)=0 or isEmpty(vInput) or isNull(vInput) or lenb(vInput)=0 then isNothing = true : end if
end function

Answer 9

You may be able to just use Else to catch nulls, ""s, etc.
If UCase(Rs("myField")) = "THING" then
'Do Things
elseif UCase(Rs("myField")) = "STUFF" then
'Do Other Stuff
else
'Invalid data, such as a NULL, "", etc.
'Throw an error, do nothing, or default action
End If
I've tested this in my code and it's currently working. Might not be right for everyone's situation though.