Ticket #4957: variant.hpp

#ifndef BOOST_SERIALIZATION_VARIANT_HPP
#define BOOST_SERIALIZATION_VARIANT_HPP

// MS compatible compilers support #pragma once
#if defined(_MSC_VER) && (_MSC_VER >= 1020)
# pragma once
#endif

#if defined(_MSC_VER) && (_MSC_VER <= 1020)
#  pragma warning (disable : 4786) // too long name, harmless warning
#endif

/////////1/////////2/////////3/////////4/////////5/////////6/////////7/////////8
// variant.hpp - non-intrusive serialization of variant types
//
// copyright (c) 2005   
// troy d. straszheim <troy@resophonic.com>
// http://www.resophonic.com
//
// Use, modification and distribution is subject to the Boost Software
// License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
// http://www.boost.org/LICENSE_1_0.txt)
//
// See http://www.boost.org for updates, documentation, and revision history.
//
// thanks to Robert Ramey, Peter Dimov, and Richard Crossley.
//

#include <boost/mpl/front.hpp>
#include <boost/mpl/pop_front.hpp>
#include <boost/mpl/eval_if.hpp>
#include <boost/mpl/identity.hpp>
#include <boost/mpl/size.hpp>
#include <boost/mpl/empty.hpp>

#include <boost/serialization/throw_exception.hpp>

#include <boost/variant.hpp>

#include <boost/archive/archive_exception.hpp>

#include <boost/serialization/split_free.hpp>
#include <boost/serialization/serialization.hpp>
#include <boost/serialization/nvp.hpp>

namespace boost {
namespace serialization {

template<class Archive>
struct variant_save_visitor :
    boost::static_visitor<>
{
    variant_save_visitor(Archive& ar) :
        m_ar(ar)
    {}
    template<class T>
    void operator()(T const & value) const
    {
        m_ar << BOOST_SERIALIZATION_NVP(value);
    }
private:
    Archive & m_ar;
};

template<class Archive, BOOST_VARIANT_ENUM_PARAMS(/* typename */ class T)>
void save(
    Archive & ar,
    boost::variant<BOOST_VARIANT_ENUM_PARAMS(T)> const & v,
    unsigned int /*version*/
){
    int which = v.which();
    ar << BOOST_SERIALIZATION_NVP(which);
    typedef BOOST_DEDUCED_TYPENAME  boost::variant<BOOST_VARIANT_ENUM_PARAMS(T)>::types types;
    variant_save_visitor<Archive> visitor(ar);
    v.apply_visitor(visitor);
}

template<class S>
struct variant_impl {

    struct load_null {
        template<class Archive, class V>
        static void invoke(
            Archive & /*ar*/,
            int /*which*/,
            V & /*v*/,
            const unsigned int /*version*/
        ){}
    };

    struct load_impl {
        template<class Archive, class V>
        static void invoke(
            Archive & ar,
            int which,
            V & v,
            const unsigned int version
        ){
            if(which == 0){
                // note: A non-intrusive implementation (such as this one)
                // necessary has to copy the value.  This wouldn't be necessary
                // with an implementation that de-serialized to the address of the
                // aligned storage included in the variant.
                typedef BOOST_DEDUCED_TYPENAME mpl::front<S>::type head_type;
                head_type value;
                ar >> BOOST_SERIALIZATION_NVP(value);
                v = value;
                ar.reset_object_address(& boost::get<head_type>(v), & value);
                return;
            }
            typedef BOOST_DEDUCED_TYPENAME mpl::pop_front<S>::type type;
            variant_impl<type>::load(ar, which - 1, v, version);
        }
    };

    template<class Archive, class V>
    static void load(
        Archive & ar,
        int which,
        V & v,
        const unsigned int version
    ){
        typedef BOOST_DEDUCED_TYPENAME mpl::eval_if<mpl::empty<S>,
            mpl::identity<load_null>,
            mpl::identity<load_impl>
        >::type typex;
        typex::invoke(ar, which, v, version);
    }

};

template<class Archive, BOOST_VARIANT_ENUM_PARAMS(/* typename */ class T)>
void load(
    Archive & ar,
    boost::variant<BOOST_VARIANT_ENUM_PARAMS(T)>& v,
    const unsigned int version
){
    int which;
    typedef BOOST_DEDUCED_TYPENAME boost::variant<BOOST_VARIANT_ENUM_PARAMS(T)>::types types;
    ar >> BOOST_SERIALIZATION_NVP(which);
    if(which >=  mpl::size<types>::value)
        // this might happen if a type was removed from the list of variant types
        boost::serialization::throw_exception(
            boost::archive::archive_exception(
                boost::archive::archive_exception::unsupported_version
            )
        );
    variant_impl<types>::load(ar, which, v, version);
}

template<class Archive,BOOST_VARIANT_ENUM_PARAMS(/* typename */ class T)>
inline void serialize(
    Archive & ar,
    boost::variant<BOOST_VARIANT_ENUM_PARAMS(T)> & v,
    const unsigned int file_version
){
    split_free(ar,v,file_version);
}

} // namespace serialization
} // namespace boost

#endif //BOOST_SERIALIZATION_VARIANT_HPP