Hello, It appears that since 1.47 Boost.Variant has a bug that can be reproduced as follows (MSVC10, Debug mode): #include <boost/variant.hpp> #include <boost/mpl/vector/vector30.hpp> struct struct1{}; struct struct2{}; struct struct3{}; struct struct4{}; struct struct5{}; struct struct6{}; struct struct7{}; struct struct8{}; struct struct9{}; struct struct10{}; struct struct11{}; struct struct12{}; struct struct13{}; struct struct14{}; struct struct15{}; struct struct16{}; struct struct17{}; struct struct18{}; struct struct19{}; struct struct20{}; struct struct21{}; typedef boost::mpl::vector21< struct1, struct2, struct3, struct4, struct5, struct6, struct7, struct8, struct9, struct10, struct11, struct12, struct13, struct14, struct15, struct16, struct17, struct18, struct19, struct20, struct21
::type vec_type; typedef boost::make_variant_over<vec_type>::type var_type;
int main() { var_type v; v = struct21(); } The last line generates assertion in variant_impl.hpp, line 264, visitation_impl() function: "Boost.Variant internal error: 'which' out of range." According to the release notes, variant wasn't changed in 1.47, but I recalled teh following discussion: http://boost.2283326.n4.nabble.com/large-variant-performance-compared-50-ele... It seems that the above issue is somehow related to this change. Igor'.