How to synthesize std::map

Hello,

Using Boost Spirit Qi, or std::unordered_map... I am receiving
assignment errors on build.

Interestingly, I can map a Vector of Member Tuples without any compiler errors:

std::vector<boost::tuple<key_t, value_t>> ...

However attempting to map an Unordered Map does not seem to work as
well, or I need to do some additional work adapting it for Qi grammar
purposes:

std::unordered_map<key_t, value_t> ...

At least not without some help, perhaps... That or I need to do so in
one, swift rule.

Assuming:

using object_t = std::unordered_map<key_t, value_t>;
using member_t = object_t::node_type;

For example, instead of:

qi::rule<iterator_type, member_t(), skipper_type> member;
qi::rule<iterator_type, object_t(), skipper_type> object_;

And which rules being defined as:

member %= member_key >> ':' >> value_;

object_ %= '{'
    >> (member % ',')
    >> '}';

I wonder whether I need to just simplify and collapse the rules into one rule.

object_ %= '{'
    >> ((member_key >> ':' >> value_) % ',')
    >> '}';

With the compiler error being:

2>d:\dev\boost.org\boost_1_69_0\boost\spirit\home\qi\detail\assign_to.hpp(153):
error C2440: 'static_cast': cannot convert from 'const T_' to
'Attribute'
2>        with
2>        [
2>            T_=kingdom::json::key_t
2>        ]
2>        and
2>        [
2>            Attribute=std::_Node_handle<std::_List_node<std::pair<const
kingdom::json::key_t,kingdom::json::value_t>,std::_Default_allocator_traits<std::allocator<std::pair<const
kingdom::json::key_t,kingdom::json::value_t>>>::void_pointer>,std::allocator<std::pair<const
kingdom::json::key_t,kingdom::json::value_t>>,std::_Node_handle_map_base,kingdom::json::key_t,kingdom::json::value_t>
2>        ]

Thoughts? Suggestions?

Cheers,

Michael Powell