DIM and SET

Hi Guys,

Everyone knows that you can create objects using the following 2 methods:


Method 1:


Method 2:


But what exactly is the difference?

I believe that in VB, no difference at all - it's only two ways to do the same thing.

There is no difference.
But for a developer you may want to declare all your variables first, then only instantiate them when you need to use them. Hence, the reason you would do Method 2.

Cheers guys!

Also, I have found that with some classes you dont actaully need to instance them in order to use them, eg:


Is it better to create a New Instance each time? I know that it will have something to do with the Threading.

probably something with "static memory" and "heap memory" but such
stuff is beyond me so I can't really tell. I find it hard to belive that it
has to do with Threading though. what make you think that?

I presumed that when the Apartment threading model is selected, then each time a new instance is created, that instance is created on a new thread, and therefor any variables that it stores are isolated from any other instances of the same class.

I thought that it would work like this... (you gotta love these diagrams!)...



... but I might be wrong. At least you will understand what I'm getting at anyway!

this is way out of my league in VB, sorry. what make you think this
is true? on what information you base your assumptions?

It just makes sense... I'm not 100% sure, that’s why I asked you guys!

I'll have to find an advanced task-manager that shows you all of the different threads that are running, then I can see if a new thread is created each time you use the 'Dim Example as New ClassX'.

I think that VB should be able to produce a Threading model diagram of your application once you have compiled it (you know, a bit like the Relationship diagrams that you get in Access... that would be sweet!).

Something that gave me a little hunch was when I created 2 Classes without using the New command. The ActiveX Class had a Public String variable in it, and in my example application I did the following experiment...



And guess what... it said "Hello!". I thought that this was a pretty solid explanation on what the threading model looked like... so I drew that diagram.

nice, it's kind of "Shared Class" then. can't see how it's related to threading,
but it's good to know such thing exist.

... because variables can only be shared if they are on the same thread (unless you physically share them by using a SET command, and I think threads can also share variables if the varibles are held in a normal .bas module). If you specify 'New' when you Dim the class, then you cant do what I just did in the example app, therefore each class must be on a different thread (ie apartment threading). :-)

Back to the original question, there is a difference if there is any other code between the DIM and the SET statements in method 2. In method 2 the object isn't created until your code reaches the SET statement. So with method 1,

dim obj as new whatever
myvar = obj.myproperty

will work, but with method 2

dim obj as whatever
myvar = obj.myproperty 'The object isn't created yet.
set obj = new whatever

will fail.