How do I make my custom class compatible with For Each?

Question

Is it possible to make a custom container class implemented purely in VBScript (no COM objects) work with the For Each statement? If so, what methods must I expose?

Answer 1

In short, no

Why? To create an enumerable collection class to get something like

Class CTest
    ....
End Class

Dim oTest, mElement
    Set oTest = New CTest
    ....
    For Each mElement In oTest
        ....
    Next 

the class MUST follow some rules. We will need the class to expose

• A public readonly property called Count

• A public default method called Item

• A public readonly property called _NewEnum, that should return an
  IUnknown interface to an object which implements the IEnumVARIANT interface and that must have the hidden attribute and a dispatch ID of -4

And from this list or requirements, VBScript does not include any way to indicate the dispatch ID or hidden attribute of a property.

So, this can not be done

The only way to enumerate over the elements stored in a container class is to have a property (or method) that returns

• an object that supports all the indicated requirements, usually the same object used to hold the elements (fast, but it will expose too much information)

• an array (in VBScript arrays can be enumerated) holding references to each of the elements in the container (slow if the array needs to be generated on call, but does not return any non required information)