https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117410
--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> --- But without the variadic arguments, the functions have equivalent function parameter lists, so the constraints are checked. With the ellipsis, they do not have equivalent function parameter lists, so the constraints are ignored. That was specified by https://wg21.link/P2113 and implemented by r11-1571-g57b4daf8dc4ed7 Since the constraints are not checked, we can remove them without changing the meaning of the program: template <typename T = void> bool foo() { return false; } template <typename T = void> bool foo(...) { return true; } template <int = 0> bool bar() { return false; } template <int x = 0> bool bar(...) { return true; } int main() { (foo()); (bar()); } All compilers agree that this is ambiguous. I think the reason GCC rejects the original one is because it's the only compiler that correctly implements P2113.
