Object instantiation characteristics

Hi,
 
I have had this question burning in the back of my mind for some time now. When you instantiate an object (examples below), do you need to do this only once for the life of a script or does it need to be done again. For example, if I write the lines shown below at the beginning of the script will they need to be introduced again?
 
Set oFSO = CreateObject("Scripting.FileSystemObject")
Set oShell = Wscript.CreateObject("WScript.Shell")
 
I have also noticed that many people set these to 0 at some point in the script. Can this be done at the end of the script or should it be done each time after you use the script? After you set these objects to 0, will they need to be instantiated again later if you need them?
 
What is best practice when it comes to instantiating objects?
 
Thanks,
Rob

You only need to instantiate the object once for the life of the script. There may be issues around scope where you might want or need to instantiate the same object more than once, but in general it is not required. I doubt that you have seen people setting those objects to 0. I suspect instead that you have seen them set those objects equal to nothing which is not at all the same thing. That used to be a very important habit because VBScript was not particularly good about releasing memory for objects that were no longer in use. These days it is much better about doing that on it's own, but it certainly doesn't hurt anything to explicitly release the objects.

Oh right! It's early in the day for me...
 
set oShell = Nothing
set oFSO = Nothing
 
I had a feeling that was how it worked based on my experience with them. I just wanted someone to lay down the law!
 
Thank you!

When you sent an object to Nothing, you are basically remove the references your script has to the object.  This is turn will be recognized by the GarbageCollector to collect the object and finalize them which in turn will then free up the resources for the system to use elsewhere.  The only real reason to use it currently is to release an object which takes up a large amount of resources and your script still have work to do and perhaps with objects that access a database.  I know if you didn't set it to "Nothing" in the past, it could lock tables and such in the databases.
 
You see it a lot at the end of scripts, which isn't really necessary since when the script ends all the resources lose the reference anyways and are GC'ed.
 
EDIT:  I just repeated ebgreen, sorry :P

All good. Never know if I have this stuff right or not anyway, so confirmation is always welcome. :)

Thanks very much for taking the time to clarify this guys!