I am facing the problem that I have a virtual function that needs to be able to take both MatrixXf and Map<MatrixXf> (the latter because there's some memory sharing going on). MatrixBase would be the right base type (I think) , but that would require templates, and you can't use templates with virtual functions in C++.
The closest related thread I found is this thread, but Refs seem to be tied to a certain derived class, so I don't think they help in my case.

Do you have any suggestions on on how to go about this?

Thanks.

Wow!, very interesting topic. I never had that problem but I can foresee having it in a not very far future. Your question took me into doing some reading about this and I found out some very interesting articles about type erasure that I think might help. Take a look and I hope it helps. Good luck!

Answer by David Rodriguez in a stack overflow post: http://stackoverflow.com/a/7968213/1889975
An article on type erasure: http://www.artima.com/cppsource/type_erasure.html

I've researched various suggestions online regarding a workaround for the virtual template function in C++, and found these:

- Template the whole class instead of just the function. Maybe I'm missing something, but that won't work, because it only kicks the can further down the road.
- Use a Visitor pattern. That's a pretty hefty API change, so I'm not sure I want to go down that path.

In the end, for now I will drop support for Map<Matrix> and just use Matrix, thus not needing template functions.

You can use Eigen's Ref<> class for your purpose:

http://eigen.tuxfamily.org/dox-devel/cl ... _1Ref.html

A Ref<Matrix> can accept either a Matrix, a Map<Matrix> and even a Block<Matrix> without needing templates.