multi_index_container serialization of non copyable types

[Sébastien Paris <sebastien.paris@…>]

A multi_index container holding non-copyable types fails to serialize because of delayed insertion through std::pair<node_type*,bool> insert_(const Value& v,Variant variant) in multi_index_container.hpp:555 happening in void load(Archive& ar,const unsigned int version) in multi_index_container.hpp:940

The insertion should use a rvalue reference overload moving the previously loaded value.

Minimal example:

template<class Archive>
void check_serialize(Archive &ar)
{
    using non_copyable_type = std::unique_ptr<int>;
    using non_copyable_multi_index = boost::multi_index_container
        <   non_copyable_type
        ,   boost::multi_index::indexed_by
            <   boost::multi_index::hashed_unique
                <   boost::multi_index::const_mem_fun
                    <   non_copyable_type
                    ,   typename non_copyable_type::pointer
                    ,   &non_copyable_type::get
                    >
                >
            >
        >;

   non_copyable_multi_index mu; // fine
   
   if constexpr (Archive::is_saving::value)
        ar << boost::serialization::make_nvp("mu",mu); // fine
   else
        ar >> boost::serialization::make_nvp("mu",mu); // error
}

[Sébastien Paris <sebastien.paris@…>]

Proposed resolution: modify multi_index_container.hpp:954-955 from

      std::pair<node_type*,bool> p=insert_(
        value.get(),super::end().get_node());

to

      std::pair<node_type*,bool> p=insert_(
        value.get(),super::end().get_node(),detail::rvalue_tag());

[Joaquín M López Muñoz]

Hi Sébastien,

Thank you for the bug report. Also, your proposed fix is correct.

It's going to take me a couple of days till I find the time to change this in develop. As we're now closing Boost 1.67, the change will go in Boost 1.68.

Best regards,

[Joaquín M López Muñoz]

Fixed at:

​https://github.com/boostorg/multi_index/commit/4d21e8962151d7d6852c5bc861a2f09fed060be5