How to obtain storage options from Eigen::MatrixBase<Derived>

I am writing template function which should take some Eigen::MatrixBase<Derived> as input, perform some computations, and then return new eigen value. I want to return value with same storage order as input.

But i have no idea how to obtain storage order from Eigen::MatrixBase<Derived>. What can i do in this situation, and is it possible at all? I know that i can pass storage order as another template parameter, or receive Eigen::Matrix<InpScalar, InpStatRows, InpStatCols, InpStorageOrder>, but i want avoid it, if it possible

PS Sorry for my poor English

Solution

To see the storage order of MatrixBase<Derived>, you can check the IsRowMajor enum:

int const StorageOrder = Derived::IsRowMajor ? Eigen::RowMajor : Eigen::ColMajor;

If you want to have a type with the same storage order and same size as Derived you can directly use typename Derived::PlainObject (or PlainMatrix):

template<class Derived>
typename Derived::PlainObject foo(const Eigen::MatrixBase<Derived> & input)
{
   typename Derived::PlainObject return_value;
   // do some complicated calculations
   return return_value;
}