/* The following code example is taken from the book * "C++ Templates - The Complete Guide" * by David Vandevoorde and Nicolai M. Josuttis, Addison-Wesley, 2002 * * (C) Copyright David Vandevoorde and Nicolai M. Josuttis 2002. * Permission to copy, use, modify, sell and distribute this software * is granted provided this copyright notice appears in all copies. * This software is provided "as is" without express or implied * warranty, and with no claim as to its suitability for any purpose. */#include <iostream>#include "funcptr.hpp"#include "compose6.hpp"#include "composeconv.hpp"double add(double a, double b) {    return a+b;}double twice(double a) {    return 2*a;}int main() {    std::cout << "compute (20+7)*2: "              << compose(func_ptr(add),func_ptr(twice))(20,7)              << '\n';}