https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57607
--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> --- Seems to be fixed in GCC 5 though: l.mm: In function ‘int main()’: l.mm:10:23: error: cannot find interface declaration for ‘NXConstantString’ std::cout << [@"Hello world!" UTF8String] << std::endl; ^