哪个编译器符合标准？

Question

Given this snippet:

template <std::size_t Index, typename T, typename ...Args>
typename type_at<Index, T, Args...>::type
get(T t1, Args... args)
{
        return 
                static_cast<type_at<Index, T, Args...>::type>
                (
                        reinterpret_cast<void*>
                        (
                                value_at<Index, T, Args...>::get(t1, args...)
                        )
                );
}


int main()
{
        int   * a     = new int(10);
        double* b     = new double(3.14);
        std::string c = "But I'm a string :(";

        std::cout<< *get<0>(a, b, &c) <<"\n";
        std::cout<< *get<1>(a, b, &c) <<"\n";
        std::cout<< *get<2>(a, b, &c) <<"\n";
}

that doesn't work on GCC 4.8.1 but compiles and runs fine in VS2012 with the Nov CTP compiler ( didn't try clang by the way )

Which compiler is right?

full example

Answer 1

In this particular case GCC is more standard compliant as you are missing typename when referring to a dependent type in type_at<Index, T, Args...>::type part of your code.

Clang is also doing a similar thing and gives a nice error message (as always):

./test.cc:40:29: error: missing 'typename' prior to dependent type name 'type_at<Index, T, Args...>::type'
                static_cast<type_at<Index, T, Args...>::type>
                            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
                            typename 
1 error generated.