Automatic Differentiation with CoDiPack

The following code:

#include <codi.hpp>
...
codi::RealForward Gcodi[l];
for (int p = 0; p < l; p++) {
     ...
     double a = Gcodi[p];
}

gives me the compilation error:

nnBFAD.cpp: In function ‘void OptBF()’:

nnBFAD.cpp:156:25: error: cannot convert ‘codi::RealForward {aka codi::ActiveReal >}’ to ‘double’ in initialization double

a = Gcodi[p];

Hints?