c – 使用元编程的私有成员存在测试,GCC vs clang,这是对的吗？

template <typename T>
class has_Data
{
   typedef char one;
   typedef long two;

   template <typename C> static one test( typeof(&C::Data) ) ;
   template <typename C> static two test(...);

public:
   enum { value = sizeof(test<T>(0)) == sizeof(char) };
};

class MyClass {
private:
   struct Data {
   };
};


void function(bool val = has_Data<MyClass>::value) {}

上面的代码适用于gcc(GCC)4.4.3

但是对于clang 3.3版(2545b1d99942080bac4a74cda92c620123d0d6e9)(2ff97832e593926ea8dbdd5fc5bcf367475638a9)

它给出了这个错误：

test_private_data.cpp:7:54: error: 'Data' is a private member of 'MyClass'
   template <typename C> static one test( typeof(&C::Data) ) ;
                                                     ^
/devshared/home/rhanda/test_private_data.cpp:7:37: note: while substituting explicitly-specified template arguments into function template 'test'
   template <typename C> static one test( typeof(&C::Data) ) ;
                                    ^
/devshared/home/rhanda/test_private_data.cpp:21:26: note: in instantiation of template class 'has_Data<MyClass>' requested here
void function(bool val = has_Data<MyClass>::value) {}
                         ^
1 error generated.

哪一个是对的？

从标准文件(n3485),我发现一个声明似乎比gcc更赞同clang.

Access control is applied uniformly to all names,whether the names are referred to from declarations or expressions.