Can I inherit my own classes from MatrixBase<T> with stable concept? (i.e. stable, public requirements)

If yes, where can I find the concept details?
Is it a good idea in general?

Probably not a good idea as the evaluation mechanism of Eigen's expressions will change from 3.2 to 3.3. What was your motivation for doing so? Maybe there is a better alternative...

ggael wrote:Probably not a good idea as the evaluation mechanism of Eigen's expressions will change from 3.2 to 3.3. What was your motivation for doing so? Maybe there is a better alternative...

This is why: https://forum.kde.org/viewtopic.php?f=74&t=127454

I wanted that the user can make any type he wants to be an Eigne Matrix expression, without extra conversion/copy.

I ended up copy data and converting manually, but I think it could be a nice feature. (I know that making a stable template concept is hard)

So, do you think it's a good idea?

oh, so you essentially wanted to write wrappers from non standard storage layout? Note that if the storage layer is such that the (i,j) can be accessed as:

*(base_ptr + i*row_stride + j*col_stride)

then you can use Map for that, no need to write a wrapper. If that's not the case, then the minimum to implement is something like:

Code: Select all

template<> Eigen::internal::traits<MyWrapper> {
 : public traits<Eigen::Matrix<list of options that are as close as possible to MyWrapper> >
  enum {
    Flags = 0 or RowMajorBit;
 };
};
class MyWrapper : public MatrixBase<MyWrapper> {
public:
  typedef MatrixBase<MyWrapper> Base;
  EIGEN_GENERIC_PUBLIC_INTERFACE(MyWrapper)
  Index rows() const;
  Index cols() const;
  Scalar coeff(i,j) const;
};


and of course, MyWrapper can be a template class too.