C++: Cast std::function to gsl_function

I want to use the GNU Scientific Library and need to cast std::function to the gsl_function, which is of type double (* function) (double x, void * params).

Until now I simply tried:

class Numerics {
 public:
  ....
  double integrate(function<double(double)> &func) {
    double result, error;
    gsl_function F;
    F.function = static_cast<(*)(double, void *)>( func );
    gsl_integration_qag(&F, 0, 1, epsabs_, epsrel_, 1000, 6, w_, &result, &error);
    return result;
  }
  ...
};

, which hands me back the error

type name requires a specifier or qualifier