object - Declaring Variables Memory Leaks

Question

I am wondering what would be the most correct way to deal with memory when using VBScript. Should declare all variables right before I use them? The beginning of the program? I understand global vs local, however in my script all variables are local. I know that memory leaks will never be a problem when writing in VBScript 99.9% of the time, but I am also curious as to the 'best' way to clear and release memory within a script. By 'best' I mean, the timing of clearing variables/objects (right after you are done using them vs the end of the script), etc.

An example:

Dim fso: Set fso = CreateObject("Scripting.FileSystemObject")
Dim arrList : Set arrList = CreateObject("System.Collections.ArrayList")
Dim objDict: Set objDic  = CreateObject( "Scripting.Dictionary")
Dim objEmail : Set objEmail = CreateObject("CDO.Message")

Dim someArray(), x, y, z, item

Answer 1

It's best practice to declare all variables, but not for the reason you assume. VBScript is sufficiently good at cleaning up after itself, so memory leaks usually aren't an issue. Most of the time you don't even need to release objects (Set var = Nothing) because they're automatically destroyed when leaving the context.

The reason why you still want to declare your variables is that you want to use Option Explicit in your scripts (which enforces variable declarations), so that you can avoid problems due to mistyped or otherwise uninitialized variables. Without Option Explicit VBScript would automagically create missing variables and initialize them with an empty/zero value. Silly example:

Dim foo : foo = 3
Dim bar : bar = 1
Do
  bar = bar + fo     'mistyped variable, initilized as empty/0
Loop Until bar > 10
WScript.Echo bar

Running the above would create an infinite loop. If you add Option Explicit the script will instead immediately terminate with a runtime error:

C:pathoyour.vbs(5, 3) Microsoft VBScript runtime error: Variable is undefined: 'fo'