id,summary,reporter,owner,description,type,status,milestone,component,version,severity,resolution,keywords,cc
12423,fusion::make_map breaks when passing references,oleg00@…,Joel de Guzman,"When using variadic maps the following code doesn't compile:

{{{
int i = 0;
fusion::make_map<int>(ref(i));
}}}


Clang gives this error:
error : no matching constructor for initialization of 'detail::map_impl<0, pair<int, int &> >'
1>            : base_type(first, rest...)
1>              ^         ~~~~~

There is a constructor in fusion::pair that can do the required conversion:
 
{{{
       template <typename Second2>
        BOOST_FUSION_GPU_ENABLED
        pair(Second2&& val
          , typename boost::disable_if<is_lvalue_reference<Second2> >::type* /* dummy */ = 0
          , typename boost::enable_if<is_convertible<Second2, Second> >::type* /*dummy*/ = 0
        ) : second(BOOST_FUSION_FWD_ELEM(Second, val)) {}

}}}


But it's not being invoked since there's no make_map function that takes rvalue refs. I was able to make this work by adding another make_map overload:


{{{
   template <typename ...Key, typename ...T>
    BOOST_CONSTEXPR BOOST_FUSION_GPU_ENABLED
      inline map<
      fusion::pair<
      Key
      , typename detail::as_fusion_element<T>::type
      >...>
      make_map(T &&... arg)
    {
      typedef map<
        fusion::pair<
        Key
        , typename detail::as_fusion_element<T>::type
      >...>
        result_type;

      return result_type(std::forward<T>(arg)...);
    }

}}}

",Bugs,new,To Be Determined,fusion,Boost 1.61.0,Problem,,fusion make_map,