[boost] boost::serialization optional does not use boost::serialization::access

21 Jul 2019

      Hi, this simple program will not compile. The only way to make it
work is to make a public default constructor. This defeats the purpose
of boost::serialization::access.

I tried to fix <boost/serialization/optional.hpp> but I couldn't get
it to correctly call the access::construct();

Please help.

// g++ -o serialize_optional /tmp/serialize_optional.cpp -lboost_serialization

#include <fstream>
#include <iostream>
#include <boost/serialization/nvp.hpp>
#include <boost/serialization/serialization.hpp>
#include <boost/archive/xml_iarchive.hpp>
#include <boost/archive/xml_oarchive.hpp>
#include <boost/serialization/access.hpp>
#include <boost/archive/text_oarchive.hpp>
#include <boost/archive/text_iarchive.hpp>
#include <boost/serialization/optional.hpp>
#include <boost/optional.hpp>

class Foo {
	public:
		Foo(int k) : i(k) {}
		friend std::ostream& operator<<(std::ostream& os, Foo const& foo) {
			return os << "Foo { " << foo.i << " }";
		}
	private:
		Foo() : i(-1) {};
		friend class boost::serialization::access;

		template<class Archive>
		void serialize(Archive & ar, const unsigned int){
			#define N(a) BOOST_SERIALIZATION_NVP(a)
			ar & N(i);
			#undef N
		};
		int i;
};

int main() {
	using Data = boost::optional<Foo>;
	std::cout << "Boost version: " << BOOST_VERSION << "\n";
	{
		auto f = Data(133);
		std::ofstream os("test.xml");
		boost::archive::xml_oarchive oa(os);
		oa << boost::serialization::make_nvp("f", f);
	}
	{
		Data g;
		std::ifstream is("test.xml");
		boost::archive::xml_iarchive ia(is);
		ia >> boost::serialization::make_nvp("f", g);

		std::cout << g.get() << "\n";
	}
}

best regards
Janek Kozicki