luabind and std::multimap

Hi everyone, sorry for sending this mail but i wasnt able to find the 
answer anywhere else.

I dont want to make a wrapper around multimap or convert the data to a 
table as this brings
useless copying of data, so the idea was to export the std::pair class 
and use it as it is
from multimap iterators. The ::first is working just fine and outputs 
the data stored as a key, but
the ::second fails and i am unable to figure out why. Can anyone maybe 
at least say that this is
not possible so i can stop banging my head against the wall? :) Thank 
you in advance...

// c++ part
std::multimap<std::string, std::string> m_multimap;

luabind::module(pLuaState)
[
	luabind::class_< std::pair<const std::string, std::string> > 
("MultimapPair")
	.property("key", &std::pair<const std::string, std::string>::first )
	.property("val", &std::pair<const std::string, std::string>::second )
];

luabind::module(pLuaState)
[
	luabind::class_<CTest>("CTest")
	.def_readwrite("multimap", &CTest::m_multimap, 
luabind::return_stl_iterator)
];

// luapart
function testclass( ctest )
   for data in ctest.multimap do
      trace(data.key)
      trace(data.value)
   end
end



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