Hello, I feel almost silly asking this but: I can only get the code listed below to compile if I remove the comments on the namespace statements, placing my custom operator<< in the boost::detail::variant namespace. Otherwise I get the error c:\Boost\include\boost-1_32\boost\variant\detail\variant_io.hpp(64) : error C2679: binary '<<' : no operator found which takes a right-hand operand of type 'const T1' (or there is no acceptable conversion) from VC++ 7.1 and a similar error from both gcc 3.3 and 3.4. I'm using boost 1.32 on both WinXP and FreeBSD. Looking at the code in variant_io.hpp, I see no reason why it should not work without the namespace statements. Is there something fundamental about namespaces that I don't understand? Thanks, -Matt #include <vector> #include <string> #include <iostream> #include <boost/variant.hpp> typedef std::vector<std::string> strlist; typedef boost::variant<int, strlist> ConfigItem; //namespace boost { namespace detail { namespace variant { inline std::ostream& operator<< (std::ostream& os, const strlist& slist) { strlist::const_iterator it; for (it=slist.begin(); it!=slist.end(); ++it) os << *it << ", "; return os; } //}}} //using namespace boost::detail::variant; void main (void) { strlist sl; std::cout << sl << std::endl; //compiles fine ConfigItem v; std::cout << v << std::endl; // error no operator found }