Question

The following code compiles with GCC 4.7 and clang 3.0, but not with MSVC 10:

template <typename X>
struct point
{
    template <typename Seq>
    struct point_iterator
    {
        template <typename T> 
        struct deref;

        template <typename Sq>
        struct deref<point_iterator<Sq> >
        {
        };
    };
};

int main()
{
    typedef point<int> point_t;
    typedef point_t::point_iterator<point_t> Iterator;
    Iterator::deref<Iterator> m;
}

The compiler error that MSVC gives is:

test.cpp
testcpp(21) : error C2079: 'm' uses undefined struct 'point<X>::point_iterator<Seq>::deref<T>'
        with
        [
            X=int,
            Seq=point_t
        ]
        and
        [
            T=Iterator
        ]

I think the type in question should be defined, since it should match the partial specialization of deref.

1. Is this valid code? If so, and rejecting it is a bug on MSVC’s part, does anyone know whether the bug has already been reported?
2. If it’s a bug, does anyone know of a workaround for it?

Answer 1

The problem is that MSVC10 does not agree that you specialized the class. If you try this

    template <typename Sq>
    struct deref
    {
       typedef int basic;
    };

    template <typename Sq>
    struct deref<point_iterator<Sq> >
    {
       typedef int special;
    };

You’ll find that Iterator::deref<Iterator>::special exists with gcc, but with MS only basic exists.

I do think your code is correct.

It’s seems that only partial specialization is affected. Specializing on int works as expected.