It looks like boost/multiprecision/detail/number_base.hpp header in one of the later trunk versions has ambiguous partial specialization problem which Oracle Studio 12.4 C++ compiler detects. It can be also detected by gcc-4.8.2 as small 35 lines independent test case below made from this header shows.
gcc -c -std=c++11 t.cc # gcc-4.8.2 compilation t.cc:17:62: error: ambiguous class template instantiation for 'struct canonical_imp<number<cpp_dec_float<50u>, (expression_template_option)1u>, cpp_dec_float<50u>, int_<3> >'
Going back to the original code rather than the reduced case, the final int_<3> implies that the first template argument (number<cpp_dec_float<50u> in this case) is convertible to const char* - and that should definitely *not* be the case. To put it another way, the error message could be a lot better (maybe I'll add a static assert for this special case), but the ambiguity is justified because: is_convertible<number<cpp_dec_float<50u> >, const char*>::value should never be true, and if it is, the code genuinely doesn't know what to do. So is there a compiler bug effecting is_convertible? Do the type_traits tests pass? Merry Christmas, John. P.S. we will have to figure out a Boost.Config setup for this new compiler release as well - really great that Sun have revitalised their compiler with C++11 support.