| #include <Eigen/Core> |
| #include <iostream> |
| using namespace Eigen; |
| using namespace std; |
| |
| template<typename Derived> |
| Eigen::VectorBlock<Derived, 2> |
| firstTwo(MatrixBase<Derived>& v) |
| { |
| return Eigen::VectorBlock<Derived, 2>(v.derived(), 0); |
| } |
| |
| template<typename Derived> |
| const Eigen::VectorBlock<Derived, 2> |
| firstTwo(const MatrixBase<Derived>& v) |
| { |
| return Eigen::VectorBlock<Derived, 2>(v.derived(), 0); |
| } |
| |
| int main(int, char**) |
| { |
| Matrix<int,1,6> v; v << 1,2,3,4,5,6; |
| cout << firstTwo(4*v) << endl; // calls the const version |
| firstTwo(v) *= 2; // calls the non-const version |
| cout << "Now the vector v is:" << endl << v << endl; |
| return 0; |
| } |