TwinBasic

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That would mean you could only use types that had a constant defined rather than any type, how would you deal with custom classes etc. in your approach?

Yes, it's a lot of trouble and I don't have a good solution at the moment. My initial thoughts are this:
All custom types (can only be classes, not UDT/Structure) are registered in my system as strings, for example:

"Of____MyClass1" represents class MyClass1
"Of____MyClass2" represents class MyClass2

But in practice, My transpiler interpret MyClass1 and MyClass2 as Object types

IMHO that would confuse the actual parameters with the type parameters though.

Yes, but the addition of type parameters complicates things.

Just looking at your suggested Constructor again... Would you expect the constructor to use the vType and vTagType parameters or would this be done by the compiler / runtime? I suspect I am not quite understanding the approach your Constructor is taking.

This constructor function of mine is not really a constructor, my transpiler automatically generates a New_List function based on the Constructor function.