14/8 says my code is right, compiler says it's wrong

Hello everybody!

I have got some code which is supposed to compile, but it doesn't. My
assumption that it "is supposed to compile" is based on 14/8 of the 2003 C++
standard, which says: "A non-exported template must be defined in every
translation unit in which it is implicitly instantiated (14.7.1), unless the
corresponding specialization is explicitly instantiated (14.7.2) in some
translation unit;[...]". The important part of this sentence is the second
one, which says, according to my understanding, that if a (non-exported)
template is explicitly specialized, it only needs to be instantiated in
"some" translation unit. Now let's look at my code:

// ---------- begin file "item.h" ----------
template <class T> struct item_traits;

template <class T> class Item
{
public:
    typedef item_traits< Item<T> > traits_type;
    int foo() { return traits_type::foo(); } // Error C2027
};
// ---------- end file "item.h" ----------

// ---------- begin file "item.cpp"----------
#include "item.h"

template <class T> struct item_traits {};

template <> struct item_traits< Item<int> >
{
    static int foo() { return 42; }
};
// ---------- end file "item.cpp" ----------

// ---------- begin file "main.cpp" ----------
#include <iostream>
#include "item.h"

int main()
{
    Item<int> x;
    std::cout << x.foo() << std::endl;
    return 0;
}
// ---------- end file "main.cpp" ----------

When I compile this on Visual C++ 2005 Express Edition, I get an error C2027
for using an undefined type "item_traits<T>" with "T=Item<int>" in file
"item.h" for the line that says:

int foo() { return traits_type::foo(); } // Error C2027

Note that item_traits< Item<int> > is explicitly specialized in file
"item.cpp", and the passage quoted from the standard at the beginning of
this post seems to says that this is all that's needed. What's wrong here?

--
Matthias Hofmann
Anvil-Soft, CEO
http://www.anvil-soft.com - The Creators of Toilet Tycoon
http://www.anvil-soft.de - Die Macher des Klomanagers

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