And C++ classes merely compile to C methods with mangled names that also take a pointer to a C struct, the first member of which is a pointer to an array of such functions, and whose remaining members are the fields.

If you (or GP) are going to argue that C++ is no more productive than C simply because cfront turns C++ into C, then I think theory has gotten in the way of reality.

I think the key difference is if the language feature automates a kind of abstraction that was manual in the other language. For example, one can write object-oriented programs in C, but you have to do it all yourself. And C++ programs can, as you pointed out, be translated to equivalent C programs. But classes and objects in C++ are language level abstractions that don't exist in C. In that regard, I agree with you: if you want to do OO programming, one can be more productive in C++ than C.

I have read much detail about Extend, but to me, the key question becomes: does it have language level abstractions that Java does not? I think closures and anonymous functions qualify, but I don't know if they're enough to make that much of a difference.

But what I've seen of Extend, with the exception of closures and anonymous functions, it doesn't actually have any new abstractions. It just cleans up the syntax.

It doesn't have any new abstractions except for those two really useful ones. Oh, ok, but it other than those it doesn't have any new ones. =)

Eh. I was arguing the direct opposite. I have the feeling that you're just looking to pick a fight.