inheriting from class of specialized self?

Question

Is this valid C++?

template
class any_iterator : public any_iterator
{ 
public:
        typedef any_iterator an         


        

Answer 1

To inherit from a type, that type must be complete. A little rearranging solves things:

template<class category>
class any_iterator;

template<>
class any_iterator<void>
{ 
public:
    typedef any_iterator<void> any_iter_void;

    any_iterator() { }
    void foo() { }
};

template<class category>
class any_iterator : public any_iterator<void>
{ 
public:
    typedef any_iterator<void> any_iter_void;

    any_iterator() : any_iter_void() { }
};

int main()
{
    any_iterator<int> a;
    a.foo();
}

---

Token standard quotes:

C++11, §10/2:

The type denoted by a base-type-specifier shall be a class type that is not an incompletely defined class; this class is called a direct base class for the class being defined.

§9.2/2:

A class is considered a completely-defined object type (or complete type) at the closing } of the class-specifier.

Answer 2

10/2:

The type denoted by a base-type-specifier shall be a class type that is not an incompletely defined class

It is one manifestation of the bug of MSVC: its lack of two-phase name resolution.