How to get available classes at runtime - forms

Question

I would like to poll a class and have it return all available subclasses in a way I can then address them. It can return an array, a dictionary, or something else. As long as I can then loop through the set of them and read properties or call functions from each.
Scenario:
I want to create a form where the user inputs the details of a series of events. Then I read the form and output a report. Each kind of event has a ".Name", but a different set of inputs (FormOptions) and methods (FormatOutput) to create an output. Right now this is implemented with a complex form and a script that runs after the user submits the form.
The trouble is that every time I add an option to the form, I have to change code in several different places. In the interest of making my code easier to maintain, I would like to contain all the code for each event type in a Class, then build the form based on the available Classes.
So as an example, I'm building an itinerary from a collection of Meeting and Travel objects:
Class Itinerary
Class Event
Public Property Get Name()
Name = "Meeting"
End Property
Public Function FormOptions(id)
Form Options = "<div id="& id &">form code for Meeting options</div>"
End Function
Public Sub FormatOutput(Time, Title, Location)
'Make a fancy meeting entry
End Sub
End Class
Class Travel
Public Property Get Name()
Name = "Travel"
End Property
Public Function FormOptions(id)
Form Options = "<div id="& id &">form code for Travel options</div>"
End Function
Public Sub FormatOutput(StartTime, EndTime, Origin, Destination)
'Make a fancy travel entry
End Sub
End Class
End Class
When the script runs it creates a form where the user can add a series of events. Each time the user chooses between "Meeting" and "Travel" then fills out the options for that event type. At the end, they push a button and the script makes a pretty document listing all the user's inputs.
At some point in the future, I will want to add a new kind of event: lodging.
Class Lodging
Public Property Get Name()
Name = "Lodging"
End Property
Public Function FormOptions(id)
Form Options = "<div id="& id &">form code for Lodging options</div>"
End Function
Public Sub FormatOutput(Date, Location)
'Make a fancy Lodging entry
End Sub
End Class
How do I setup my Itinerary class so that it automatically recognizes the new class and can return it as an available event type? I can think of several ways of doing this, but they all involve keeping an index of the available classes separate from the actual classes, and I'm trying to minimize the number of places I have to change code when I add new event types.
I am very purposely not including any details on how I build the form since at this point I'm open to anything. Also, please be gentle with references to "inheritance", "extensibility", or "polymorphism". I'm a just a scripter and these OOP concepts are still a bit foreign to me.

Answer 1

I don't think this is possible, but one way to come close to this would be to have a unique list of class names -- the simplest would be to have a global dictionary.
You can get a list of classes by reading the Keys collection of the dictionary.
I don't think VBScript supports references to classes, so when the user chooses one of the types use Eval to create an instance of the appropriate class.
Dim ClassList
Set ClassList = CreateObject("Scripting.Dictionary")
'on type selection:
Function GetItineraryInstance(className)
Set GetItineraryInstance = Eval("New " & className)
End Function
ClassList("Travel") = 1
Class Travel
'methods
End Class
At least the class registration can be kept together with the class definition.