using + template - how has this been resolved?

[Helmut Jarausch]

Hi,

there is the following example in Vandevoorde/Josuttis
C++ Templates (7th printing) ch 9.3.4 p 134

template <typename T>
class BXT {
public:
typedef T Mystery;
template<typename U>
struct Magic;
};

template <typename T>
class DXTM : private BXT<T> {
public:
// using BXT<T>::template Magic; // fails
// Most likely this is an oversight in the standard specifications
// and future revisions will probably make the previous construct valid

// using BXT<T>::Magic; // fails
Magic<T>* plink;
};

How has this been resolved?

Many thanks for some info.

Helmut Jarausch
Lehrstuhl fuer Numerische Mathematik
RWTH - Aachen University
D 52056 Aachen, Germany

 

[Johannes Schaub (litb)]

Hi,

there is the following example in Vandevoorde/Josuttis
C++ Templates (7th printing) ch 9.3.4 p 134

template <typename T>
class BXT {
public:
typedef T Mystery;
template<typename U>
struct Magic;
};

template <typename T>
class DXTM : private BXT<T> {
public:
// using BXT<T>::template Magic; // fails
// Most likely this is an oversight in the standard specifications
// and future revisions will probably make the previous construct valid

// using BXT<T>::Magic; // fails
Magic<T>* plink;
};

How has this been resolved?

It has not been resolved, and probably won't be resolved. See
http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_closed.html#109

 

[Johannes Schaub (litb)]

Hi,

there is the following example in Vandevoorde/Josuttis
C++ Templates (7th printing) ch 9.3.4 p 134

template <typename T>
class BXT {
public:
typedef T Mystery;
template<typename U>
struct Magic;
};

template <typename T>
class DXTM : private BXT<T> {
public:
// using BXT<T>::template Magic; // fails
// Most likely this is an oversight in the standard specifications
// and future revisions will probably make the previous construct valid

// using BXT<T>::Magic; // fails
Magic<T>* plink;
};

How has this been resolved?

What I've previously overlooked: I think you *can* say the following,
though. It is the name of a member template. Not the name of a member
template specialization.

using BXT<T>::Magic;

The error is at the point of use, because it does not know whether Magic
refers to a class template or not.

typename DXTM<T>::template Magic<T> *plink;