函数模板中的decltype和scope resolution运算符

Question

Apparently, the following code does not compile on gcc 4.7:

#include <vector>

struct foo {
    std::vector<int> x;

    template<typename T>
    void bar(T) {
        decltype(x)::value_type y;
    }
};

int main() {
    foo f;
    f.bar(0);
}

The compilation error is the following:

test.cpp:8:9: error: need ‘typename’ before ‘decltype (((foo*)this)->foo::x)::value_type’ because ‘decltype (((foo*)this)->foo::x)’ is a dependent scope

I know the solution to the problem, but why is it not compiling? x here is not a dependent name, so why do I need to explicitly indicate that decltype(x)::value_type is a type if the compiler can already figure that out by himself? Or am I wrong and x is actually a dependent name here?

Answer 1

Until someone finds a specific report on this (I tried looking and the closest I've found is this ), this does compile with GCC 4.8.0 . Based on that information and my prior suspicions, I would say this is just a bug in GCC 4.7 that was fixed for 4.8.