How does the existence of RTTI falsify the statement "you can't tell the class of a C++ object given a pointer to it at run time"? Not all objects are instances of classes with vtables.
Because RTTI lets you tell the class of a C++ object given a pointer to it at run time. The statement was false. This is not a subtle argument.
Again, you're trying to set up a straw man: the question is not whether or not it's efficient to do type inference in C++ (for the record: it's NOT any more efficient in a dynamic language), the question is whether it's possible at all.
It is possible to do so, the original argument was incorrect, and you're trying to have an entirely different debate.
Yes, I know. You're arguing that not all classes have vtables. I'm arguing that there's no reason that they can't, save for efficiency concerns. And if you're so concerned about efficiency that vtables are a burden, then you're already in a situation where an interpreted language is inappropriate for your needs.
Now you're arguing something different. Just because all classes can, doesn't mean that they do, or that a general purpose tool (like, say, a garbage collector) can assume that they do. It's not a question of efficiency, it's a question of what the language allows. If you're saying "everything has to have a vtable", then you aren't talking about C++.
