CPP13 — C++ _var type widening proposal

Summary: Michi Henning & Steve Vinoski have previously challenged people to come
up with a modification to the C++ language mapping that would allow for
type safe widening of object reference _var types for assignment or copy
construction. I believe I have come up with the solution, and Michi
agrees with me:

Proposal:

For object reference _var types, replace the copy and assignment
operators:

class T_var

;

with:

class T_var {
public:
...
template <class C_var>
T_var(const C_var &cv) : ptr_(T::_duplicate(cv.in()) {
}

template <class C_var>
T_var &operator = (const C_var &cv) {
if ((void *)this != (void *)cv)

return *this;
}
...
private:
T_ptr ptr_;
};