https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101904
--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> --- (In reply to Jonathan Wakely from comment #3) > I think Clang doesn't even bother to instantiate the return type for the > non-const overload, because it wouldn't be viable. I'm not sure if that's a > conforming implementation or not. [temp.inst] p9: "If the function selected by overload resolution (12.2) can be determined without instantiating a class template definition, it is unspecified whether that instantiation actually takes place." So the compiler is permitted to skip the result_of instantiation in the return type if it knows that overload won't be selected anyway. But it's not required to skip it, so your code is still wrong.
