http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48891
--- Comment #6 from Marc Glisse <marc.glisse at normalesup dot org> 2012-04-29 13:15:40 UTC --- I don't think it matters that much whether the return type is int or bool, compared to the inconvenience of having 2 functions that conflict. The constexpr qualifier is nice, but not required by the standard, and not even by gcc which recognizes that extern "C" int isnan(double) is a builtin (note that it doesn't recognize it anymore if you change the return type to bool, that should be fixed). For the same reason (recognized as a builtin), there is no performance advantage to having it inline. So I think: * glibc could change the return type of isnan to bool in C++ (there would be a regression in that ::isnan wouldn't be constexpr and inline until g++ is taught the right prototype) * libstdc++ could import ::isnan in std::, assuming isnan exists. Maybe that requires a configure test. Maybe that test would be rather fragile (depends on feature macros). Maybe that's where this stops being a good idea :-(
