VBScript conditional short-circuiting workaround

asp-classicvbscript

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?

Best Answer

Nested IFs (only slightly less verbose):

if not isNull(Rs("myField")) Then
   if Rs("myField") <> 0 then

Related Solutions

ASP/VBScript – Int() vs CInt()

Int()

The Int function returns the integer part of a specified number.

CInt()

The CInt function converts an expression to type Integer.

And the best answer comes from MSDN

CInt differs from the Fix and Int functions, which truncate, rather than round, the fractional part of a number. When the fractional part is exactly 0.5, the CInt function always rounds it to the nearest even number. For example, 0.5 rounds to 0, and 1.5 rounds to 2.

Get the type of a variable in VBScript

Is VarType what you need?

Returns a value indicating the subtype of a variable.

+--------------+-------+---------------------------------------------+
|   Constant   | Value |                 Description                 |
+--------------+-------+---------------------------------------------+
| vbEmpty      |     0 | Empty (uninitialized)                       |
| vbNull       |     1 | Null (no valid data)                        |
| vbInteger    |     2 | Integer                                     |
| vbLong       |     3 | Long integer                                |
| vbSingle     |     4 | Single-precision floating-point number      |
| vbDouble     |     5 | Double-precision floating-point number      |
| vbCurrency   |     6 | Currency                                    |
| vbDate       |     7 | Date                                        |
| vbString     |     8 | String                                      |
| vbObject     |     9 | Automation object                           |
| vbError      |    10 | Error                                       |
| vbBoolean    |    11 | Boolean                                     |
| vbVariant    |    12 | Variant (used only with arrays of Variants) |
| vbDataObject |    13 | A data-access object                        |
| vbDecimal    |    14 | Decimal Value                               |
| vbByte       |    17 | Byte                                        |
| vbLongLong   |    20 | LongLong integer (64 bit)                   |
| vbArray      |  8192 | Array                                       |
+--------------+-------+---------------------------------------------+

The VarType function never returns the value for Array by itself. It is always added to some other value to indicate an array of a particular type. The value for Variant is only returned when it has been added to the value for Array to indicate that the argument to the VarType function is an array. For example, the value returned for an array of integers is calculated as 2 + 8192, or 8194. If an object has a default property, VarType (object) returns the type of its default property.

Best Answer

Related Solutions

ASP/VBScript – Int() vs CInt()

Get the type of a variable in VBScript

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