[Boost-users] Variant stream output of ICU UnicodeString

Hi, I'm trying to stream a Boost::Variant with << to std::cout but when I include an UnicodeString member from the ICU Unicode library the compiler doesn't recognices my overloaded operator<< for the UnicodeString. Here is a test program: #include <iostream> #include #include class Foo {}; std::ostream& operator<<(std::ostream& stream, Foo const &b) { return stream << "Foo"; } std::ostream& operator<<(std::ostream& stream, UnicodeString const & unicode) { return stream << "Unicode"; } int main() { boost::variant test; test = Foo(); std::cout << test << std::endl; test = "Hello World"; std::cout << test << std::endl; return 0; } Without the UnicodeString code everything works find but with it I get the following errors: g++ -O0 -g3 -Wall -c -fmessage-length=0 -MMD -MP -MF"src/TestUnicode.d" -MT"src/TestUnicode.d" -o "src/TestUnicode.o" "../src/TestUnicode.cpp" In file included from /usr/include/boost/variant/variant.hpp:1859, from /usr/include/boost/variant.hpp:17, from ../src/TestUnicode.cpp:11: /usr/include/boost/variant/detail/variant_io.hpp: In member function ‘void boost::detail::variant::printer<OStream>::operator()(const T&) const [with T = icu_4_2::UnicodeString, OStream = std::basic_ostream]’: /usr/include/boost/variant/variant.hpp:825: instantiated from ‘typename Visitor::result_type boost::detail::variant::invoke_visitor<Visitor>::internal_visit(T&, int) [with T = const icu_4_2::UnicodeString, Visitor = boost::detail::variant::printer >]’ /usr/include/boost/variant/detail/visitation_impl.hpp:126: instantiated from ‘typename Visitor::result_type boost::detail::variant::visitation_impl_invoke_impl(int, Visitor&, VoidPtrCV, T*, mpl_::true_) [with Visitor = boost::detail::variant::invoke_visitor > >, VoidPtrCV = const void*, T = boost::detail::variant::visitation_impl(int, int, Visitor&, VoidPtrCV, mpl_::false_, NoBackupFlag, Which*, step0*) [with Which = boost::variant::internal_apply_visitor_impl(int, int, Visitor&, VoidPtrCV) [with Visitor = boost::detail::variant::invoke_visitor > >, VoidPtrCV = const void*, T0_ = Foo, T1 = icu_4_2::UnicodeString, T2 = int, T3 = double, T4 = boost::detail::variant::void_, T5 = boost::detail::variant::void_, T6 = boost::detail::variant::void_, T7 = boost::detail::variant::void_, T8 = boost::detail::variant::void_, T9 = boost::detail::variant::void_, T10 = boost::detail::variant::void_, T11 = boost::detail::variant::void_, T12 = boost::detail::variant::void_, T13 = boost::detail::variant::void_, T14 = boost::detail::variant::void_, T15 = boost::detail::variant::void_, T16 = boost::detail::variant::void_, T17 = boost::detail::variant::void_, T18 = boost::detail::variant::void_, T19 = boost::detail::variant::void_]::first_which, step0 = boost::variant::internal_apply_visitor_impl(int, int, Visitor&, VoidPtrCV) [with Visitor = boost::detail::variant::invoke_visitor > >, VoidPtrCV = const void*, T0_ = Foo, T1 = icu_4_2::UnicodeString, T2 = int, T3 = double, T4 = boost::detail::variant::void_, T5 = boost::detail::variant::void_, T6 = boost::detail::variant::void_, T7 = boost::detail::variant::void_, T8 = boost::detail::variant::void_, T9 = boost::detail::variant::void_, T10 = boost::detail::variant::void_, T11 = boost::detail::variant::void_, T12 = boost::detail::variant::void_, T13 = boost::detail::variant::void_, T14 = boost::detail::variant::void_, T15 = boost::detail::variant::void_, T16 = boost::detail::variant::void_, T17 = boost::detail::variant::void_, T18 = boost::detail::variant::void_, T19 = boost::detail::variant::void_]::first_step, Visitor = boost::detail::variant::invoke_visitor > >, VoidPtrCV = const void*, NoBackupFlag = boost::variant::has_fallback_type_]::T1]’ /usr/include/boost/variant/detail/visitation_impl.hpp:169: instantiated from ‘typename Visitor::result_type boost::detail::variant::visitation_impl_invoke(int, Visitor&, VoidPtrCV, T*, NoBackupFlag, int) [with Visitor = boost::detail::variant::invoke_visitor > >, VoidPtrCV = const void*, T = boost::detail::variant::visitation_impl(int, int, Visitor&, VoidPtrCV, mpl_::false_, NoBackupFlag, Which*, step0*) [with Which = boost::variant::internal_apply_visitor_impl(int, int, Visitor&, VoidPtrCV) [with Visitor = boost::detail::variant::invoke_visitor > >, VoidPtrCV = const void*, T0_ = Foo, T1 = icu_4_2::UnicodeString, T2 = int, T3 = double, T4 = boost::detail::variant::void_, T5 = boost::detail::variant::void_, T6 = boost::detail::variant::void_, T7 = boost::detail::variant::void_, T8 = boost::detail::variant::void_, T9 = boost::detail::variant::void_, T10 = boost::detail::variant::void_, T11 = boost::detail::variant::void_, T12 = boost::detail::variant::void_, T13 = boost::detail::variant::void_, T14 = boost::detail::variant::void_, T15 = boost::detail::variant::void_, T16 = boost::detail::variant::void_, T17 = boost::detail::variant::void_, T18 = boost::detail::variant::void_, T19 = boost::detail::variant::void_]::first_which, step0 = boost::variant::internal_apply_visitor_impl(int, int, Visitor&, VoidPtrCV) [with Visitor = boost::detail::variant::invoke_visitor > >, VoidPtrCV = const void*, T0_ = Foo, T1 = icu_4_2::UnicodeString, T2 = int, T3 = double, T4 = boost::detail::variant::void_, T5 = boost::detail::variant::void_, T6 = boost::detail::variant::void_, T7 = boost::detail::variant::void_, T8 = boost::detail::variant::void_, T9 = boost::detail::variant::void_, T10 = boost::detail::variant::void_, T11 = boost::detail::variant::void_, T12 = boost::detail::variant::void_, T13 = boost::detail::variant::void_, T14 = boost::detail::variant::void_, T15 = boost::detail::variant::void_, T16 = boost::detail::variant::void_, T17 = boost::detail::variant::void_, T18 = boost::detail::variant::void_, T19 = boost::detail::variant::void_]::first_step, Visitor = boost::detail::variant::invoke_visitor > >, VoidPtrCV = const void*, NoBackupFlag = boost::variant::has_fallback_type_]::T1, NoBackupFlag = boost::variant::has_fallback_type_]’ /usr/include/boost/variant/detail/visitation_impl.hpp:256: instantiated from ‘typename Visitor::result_type boost::detail::variant::visitation_impl(int, int, Visitor&, VoidPtrCV, mpl_::false_, NoBackupFlag, Which*, step0*) [with Which = boost::variant::internal_apply_visitor_impl(int, int, Visitor&, VoidPtrCV) [with Visitor = boost::detail::variant::invoke_visitor > >, VoidPtrCV = const void*, T0_ = Foo, T1 = icu_4_2::UnicodeString, T2 = int, T3 = double, T4 = boost::detail::variant::void_, T5 = boost::detail::variant::void_, T6 = boost::detail::variant::void_, T7 = boost::detail::variant::void_, T8 = boost::detail::variant::void_, T9 = boost::detail::variant::void_, T10 = boost::detail::variant::void_, T11 = boost::detail::variant::void_, T12 = boost::detail::variant::void_, T13 = boost::detail::variant::void_, T14 = boost::detail::variant::void_, T15 = boost::detail::variant::void_, T16 = boost::detail::variant::void_, T17 = boost::detail::variant::void_, T18 = boost::detail::variant::void_, T19 = boost::detail::variant::void_]::first_which, step0 = boost::variant::internal_apply_visitor_impl(int, int, Visitor&, VoidPtrCV) [with Visitor = boost::detail::variant::invoke_visitor > >, VoidPtrCV = const void*, T0_ = Foo, T1 = icu_4_2::UnicodeString, T2 = int, T3 = double, T4 = boost::detail::variant::void_, T5 = boost::detail::variant::void_, T6 = boost::detail::variant::void_, T7 = boost::detail::variant::void_, T8 = boost::detail::variant::void_, T9 = boost::detail::variant::void_, T10 = boost::detail::variant::void_, T11 = boost::detail::variant::void_, T12 = boost::detail::variant::void_, T13 = boost::detail::variant::void_, T14 = boost::detail::variant::void_, T15 = boost::detail::variant::void_, T16 = boost::detail::variant::void_, T17 = boost::detail::variant::void_, T18 = boost::detail::variant::void_, T19 = boost::detail::variant::void_]::first_step, Visitor = boost::detail::variant::invoke_visitor > >, VoidPtrCV = const void*, NoBackupFlag = boost::variant::has_fallback_type_]’ /usr/include/boost/variant/variant.hpp:1769: instantiated from ‘static typename Visitor::result_type boost::variant::internal_apply_visitor_impl(int, int, Visitor&, VoidPtrCV) [with Visitor = boost::detail::variant::invoke_visitor > >, VoidPtrCV = const void*, T0_ = Foo, T1 = icu_4_2::UnicodeString, T2 = int, T3 = double, T4 = boost::detail::variant::void_, T5 = boost::detail::variant::void_, T6 = boost::detail::variant::void_, T7 = boost::detail::variant::void_, T8 = boost::detail::variant::void_, T9 = boost::detail::variant::void_, T10 = boost::detail::variant::void_, T11 = boost::detail::variant::void_, T12 = boost::detail::variant::void_, T13 = boost::detail::variant::void_, T14 = boost::detail::variant::void_, T15 = boost::detail::variant::void_, T16 = boost::detail::variant::void_, T17 = boost::detail::variant::void_, T18 = boost::detail::variant::void_, T19 = boost::detail::variant::void_]’ /usr/include/boost/variant/variant.hpp:1791: instantiated from ‘typename Visitor::result_type boost::variant::internal_apply_visitor(Visitor&) const [with Visitor = boost::detail::variant::invoke_visitor > >, T0_ = Foo, T1 = icu_4_2::UnicodeString, T2 = int, T3 = double, T4 = boost::detail::variant::void_, T5 = boost::detail::variant::void_, T6 = boost::detail::variant::void_, T7 = boost::detail::variant::void_, T8 = boost::detail::variant::void_, T9 = boost::detail::variant::void_, T10 = boost::detail::variant::void_, T11 = boost::detail::variant::void_, T12 = boost::detail::variant::void_, T13 = boost::detail::variant::void_, T14 = boost::detail::variant::void_, T15 = boost::detail::variant::void_, T16 = boost::detail::variant::void_, T17 = boost::detail::variant::void_, T18 = boost::detail::variant::void_, T19 = boost::detail::variant::void_]’ /usr/include/boost/variant/variant.hpp:1813: instantiated from ‘typename Visitor::result_type boost::variant::apply_visitor(Visitor&) const [with Visitor = boost::detail::variant::printer >, T0_ = Foo, T1 = icu_4_2::UnicodeString, T2 = int, T3 = double, T4 = boost::detail::variant::void_, T5 = boost::detail::variant::void_, T6 = boost::detail::variant::void_, T7 = boost::detail::variant::void_, T8 = boost::detail::variant::void_, T9 = boost::detail::variant::void_, T10 = boost::detail::variant::void_, T11 = boost::detail::variant::void_, T12 = boost::detail::variant::void_, T13 = boost::detail::variant::void_, T14 = boost::detail::variant::void_, T15 = boost::detail::variant::void_, T16 = boost::detail::variant::void_, T17 = boost::detail::variant::void_, T18 = boost::detail::variant::void_, T19 = boost::detail::variant::void_]’ /usr/include/boost/variant/detail/variant_io.hpp:85: instantiated from ‘std::basic_ostream<_CharT, _Traits>& boost::operator<<(std::basic_ostream<_CharT, _Traits>&, const boost::variant&) [with E = char, T = std::char_traits<char>, U0 = Foo, U1 = icu_4_2::UnicodeString, U2 = int, U3 = double, U4 = boost::detail::variant::void_, U5 = boost::detail::variant::void_, U6 = boost::detail::variant::void_, U7 = boost::detail::variant::void_, U8 = boost::detail::variant::void_, U9 = boost::detail::variant::void_, U10 = boost::detail::variant::void_, U11 = boost::detail::variant::void_, U12 = boost::detail::variant::void_, U13 = boost::detail::variant::void_, U14 = boost::detail::variant::void_, U15 = boost::detail::variant::void_, U16 = boost::detail::variant::void_, U17 = boost::detail::variant::void_, U18 = boost::detail::variant::void_, U19 = boost::detail::variant::void_]’ ../src/TestUnicode.cpp:27: instantiated from here /usr/include/boost/variant/detail/variant_io.hpp:64: error: no match for ‘operator<<’ in ‘((const boost::detail::variant::printer

*)this)->boost::detail::variant::printer >::out_ << operand’ /usr/include/c++/4.4/ostream:108: note: candidates are: std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(std::basic_ostream<_CharT, _Traits>& (*)(std::basic_ostream<_CharT, _Traits>&)) [with _CharT = char, _Traits = std::char_traits<char>] /usr/include/c++/4.4/ostream:117: note: std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(std::basic_ios<_CharT, _Traits>& (*)(std::basic_ios<_CharT, _Traits>&)) [with _CharT = char, _Traits = std::char_traits<char>] /usr/include/c++/4.4/ostream:127: note: std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(std::ios_base& (*)(std::ios_base&)) [with _CharT = char, _Traits = std::char_traits<char>] /usr/include/c++/4.4/ostream:165: note: std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(long int) [with _CharT = char, _Traits = std::char_traits<char>] /usr/include/c++/4.4/ostream:169: note: std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(long unsigned int) [with _CharT = char, _Traits = std::char_traits<char>] /usr/include/c++/4.4/ostream:173: note: std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(bool) [with _CharT = char, _Traits = std::char_traits<char>] /usr/include/c++/4.4/bits/ostream.tcc:91: note: std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(short int) [with _CharT = char, _Traits = std::char_traits<char>] /usr/include/c++/4.4/ostream:180: note: std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(short unsigned int) [with _CharT = char, _Traits = std::char_traits<char>] /usr/include/c++/4.4/bits/ostream.tcc:105: note: std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(int) [with _CharT = char, _Traits = std::char_traits<char>] /usr/include/c++/4.4/ostream:191: note: std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(unsigned int) [with _CharT = char, _Traits = std::char_traits<char>] /usr/include/c++/4.4/ostream:200: note: std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(long long int) [with _CharT = char, _Traits = std::char_traits<char>] /usr/include/c++/4.4/ostream:204: note: std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(long long unsigned int) [with _CharT = char, _Traits = std::char_traits<char>] /usr/include/c++/4.4/ostream:209: note: std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(double) [with _CharT = char, _Traits = std::char_traits<char>] /usr/include/c++/4.4/ostream:213: note: std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(float) [with _CharT = char, _Traits = std::char_traits<char>] /usr/include/c++/4.4/ostream:221: note: std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(long double) [with _CharT = char, _Traits = std::char_traits<char>] /usr/include/c++/4.4/ostream:225: note: std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(const void*) [with _CharT = char, _Traits = std::char_traits<char>] /usr/include/c++/4.4/bits/ostream.tcc:119: note: std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(std::basic_streambuf<_CharT, _Traits>*) [with _CharT = char, _Traits = std::char_traits<char>]

I'm using gcc 4.4.5 on Ubuntu 11.04 and boost 1.42. Does someone know why the overloaded operator isn't used or how I can get the test program to work?