On 9/28/2010 10:50 PM, Adam Badura wrote:
We are using Boost 1.43.0 (we tried to move to 1.44.0 but there were some problems which I reported some time ago) in Visual Studio 2010. And there are some compilation problems when variant type objects are swapped. This does not affect all variant types but I didn't figured out what are the exact conditions (however I guess it is likely something with namespaces and templates).
Following code demonstrates the issue: ---------------------------------------- #include <cstdlib> #include <list> #include <boost/variant.hpp>
int main() { typedef boost::variant< std::list< int >::iterator > variant_type;
variant_type v; variant_type().swap( v );
return EXIT_SUCCESS; } ----------------------------------------
compilation fails with following message: ---------------------------------------- 1>d:\libraries\boost_1_43_0\boost\variant\detail\move.hpp(155): error C2668: 'boost::detail::variant::detail::move_swap::swap' : ambiguous call to overloaded function 1> d:\libraries\boost_1_43_0\boost\variant\detail\move.hpp(141): could be 'void boost::detail::variant::detail::move_swap::swap<T>(T &,T &)' 1> with 1> [ 1> T=T0 1> ] 1> c:\program files\microsoft visual studio 10.0\vc\include\utility(100): or 'void std::swap<T>(_Ty &,_Ty &)' [found using argument-dependent lookup] 1> with 1> [ 1> T=T0, 1> _Ty=T0 1> ] 1> while trying to match the argument list '(T0, T0)' [...]
Local changes you can make to get a quick fix (I hope): Try expressing the implementation of boost::detail::move_swap in terms of 2 independent template parameters, rather than 1: template <typename T,typename U> inline void swap(T& lhs, U& rhs) { T tmp( boost::detail::variant::move(lhs) ); lhs = boost::detail::variant::move(rhs); rhs = boost::detail::variant::move(tmp); } This is the same "trick" that boost::swap uses to avoid ambiguity with std::swap, I believe; see the comment in boost/utility/swap.hpp. I verified that this fixes your issue on MSVC9, at least. I don't have boost 1.44 installed (yet), but you might want to check if it looks like the same problem exists there, and if it does, file a trac ticket...? - Jeff