How to implement custom iterable class in VBA

excel class vba foreach iunknown
JayC667 picture JayC667 · Nov 25, 2013 · Viewed 7.3k times · Source

I want to add a feature to my classes so I can use them in for-each loops.

I wrote hashmaps, arraylists, queues, sets and so on that I want to iterate over. Now I'm looking for a way to implement the IUnknown class to build custom iterators.

I already know how to use 

private objPeople as Collection
Public Property Get NewEnum() As IUnknown
Attribute NewEnum.VB_UserMemId = -4
Attribute NewEnum.VB_MemberFlags = "40"
    Set NewEnum = objPeople.[_NewEnum]
End Property

but all those examples out there are based on the Collection class, which I do not want to use.

What I want to focus on is trying to implement the IUnknown interface, but I haven't found any references on how to do that.

I have vast experience in Java, C++, C# and so on, so I assume that THERE HAS TO BE A WAY to implement that even in VBA, maybe even with API calls stuff like that.

Answer

RubberDuck picture RubberDuck · Aug 27, 2014

The long and short of it is you can't implement IUnknown. The same goes for Collection. They're both Com objects that are unavailable for extension in VBA. You can create custom collections and do other very cool iterable things though.

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