Problems with "Barton Nackman Trick"

[Michael Lehn]

I want to use the "Barton Nackman trick" for my matrix hierarchy. But I ran
into a problem with a typedef I need in the base class:

template <typename E>
class Matrix
{
public:
typedef typename E::TT TT;

};

template <typename T>
class DenseMatrix : public Matrix<DenseMatrix<T> >
{
public:
typedef T TT;

};

this gives the error: no type named `TT' in `class DenseMatrix<double>'

Is there a chance to solve this problem, or is it even a comipler problem?

I think the approach is pretty useless if this doesn't work. Most (or even
all) methods in the base class will depend on the parameter "E::TT".

[Michael Lehn]

Michael Lehn wrote:

I want to use the "Barton Nackman trick" for my matrix hierarchy. But I
ran into a problem with a typedef I need in the base class:

template <typename E>
class Matrix
{
public:
typedef typename E::TT TT;

};

template <typename T>
class DenseMatrix : public Matrix<DenseMatrix<T> >
{
public:
typedef T TT;

};

this gives the error: no type named `TT' in `class DenseMatrix<double>'

Is there a chance to solve this problem, or is it even a comipler problem?

I think the approach is pretty useless if this doesn't work. Most (or
even all) methods in the base class will depend on the parameter "E::TT".

hmmm, this seems to work:

template <typename A>
struct Traits
{
};

template <typename E>
class Matrix
{
public:
typedef typename Traits<E>::TT TT;

};

template <typename T>
class DenseMatrix : public Matrix<DenseMatrix<T> >
{
public:
typedef T TT;

};

template <typename T>
struct Traits<DenseMatrix<T> >
{
typedef T TT;
};
....is this a bug or a feature?

[Michael Lehn]

So is this standard conform?