Проверка доступа в c++

#ifndef USING_SIMPLE_BASE
	#include <tuple>
	#define BASE std::tuple_element_t<0,std::tuple<base>>
#else
	#define BASE base
#endif

struct base { protected: using type = int; };

template<typename> struct derived :private BASE
{
	using BASE::type;
};

int main() { return derived<int>::type(0); }

template <std::size_t I, class T>
using tuple_element_t = typename tuple_element<I, T>::type;

cat 1.cpp
#ifndef USING_SIMPLE_BASE
	#include <tuple>
	#define BASE std::tuple_element_t<0,std::tuple<base>>
#else
	#define BASE base
#endif

struct base { protected: using type = int; };

template<typename> struct derived :private BASE
{
	using BASE::type;
};

int main() { return derived<int>::type(0); }
g++-7 -xc++ -std=c++14 -pedantic -o/dev/null 1.cpp
g++-7 -v
gcc version 7.2.0 (Ubuntu 7.2.0-1ubuntu1~16.04)

#ifndef USING_SIMPLE_BASE
	#include <tuple>
	#define BASE std::tuple_element_t<0,std::tuple<base<T>>>
#else
	#define BASE base<T>
#endif

template<typename> struct base { protected: using type = int; };

template<typename T> struct derived :private BASE
{
	using typename BASE::type;
};

int main() { return derived<int>::type(0); }

#include <tuple>
#define BASE std::tuple_element_t<0,std::tuple<base<T>>>

template<typename> struct base { protected: using type = int; };

template<typename T> struct derived :private BASE
{
	using typename BASE::type;
};

int main() 
{ 
	return derived<int>::type(0); 
}

1>------ Перестроение всех файлов начато: проект: Project134, Конфигурация: Release Win32 ------
1>main.cpp
1>Создание кода
1>All 1 functions were compiled because no usable IPDB/IOBJ from previous compilation was found.
1>Создание кода завершено
1>Project134.vcxproj -> C:\Users\fsb4000\Documents\Visual Studio 2017\Projects\Project134\Release\Project134.exe
========== Перестроение всех проектов: успешно: 1, с ошибками: 0, пропущено: 0 ==========

Ошибка	C2248	base::type: невозможно обратиться к protected typedef, объявленному в классе "base"

error: 'type' is a private member of 'base'
int main() { return derived<int>::type(0); }
                                  ^
1.cpp:10:36: note: constrained by private inheritance here
template<typename> struct derived :private BASE
                                   ^~~~~~~~~~~~
1.cpp:8:32: note: member is declared here
struct base { protected: using type = int; };
                               ^
1 error generated.

clang version 6.0.0 (trunk)
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/bin
Found candidate GCC installation: /usr/bin/../lib/gcc/i686-linux-gnu/7
Found candidate GCC installation: /usr/bin/../lib/gcc/i686-linux-gnu/7.2.0
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/7
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/7.2.0
Found candidate GCC installation: /usr/lib/gcc/i686-linux-gnu/7
Found candidate GCC installation: /usr/lib/gcc/i686-linux-gnu/7.2.0
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/7
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/7.2.0
Selected GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/7.2.0
Candidate multilib: .;@m64
Candidate multilib: 32;@m32
Candidate multilib: x32;@mx32
Selected multilib: .;@m64

$ cat test-2.cxx
#ifndef USING_SIMPLE_BASE
	#include <tuple>
	#define BASE std::tuple_element<0,std::tuple<base>>::type
#else
	#define BASE base
#endif

struct base { protected: using type = int; };

template<typename> struct derived :public BASE
{
	using BASE::type;
};

int main() { return derived<int>::type(0); }
$ 
$ clang++ -xc++ -std=c++14 -pedantic -o/dev/null test-2.cxx
test-2.cxx:15:35: error: 'type' is a protected member of 'base'
int main() { return derived<int>::type(0); }
                                  ^
test-2.cxx:8:32: note: declared protected here
struct base { protected: using type = int; };
                               ^
1 error generated.

#include <tuple>
#define BASE std::tuple_element_t<0,std::tuple<base<T>>>

template<typename> struct base { protected: using type = int; };

template<typename T> struct derived :private BASE
{
	using typename BASE::type;
};

int main() 
{ 
	return derived<int>::type(0); 
}

struct base { protected: using type = int; };

int main() { return base::type(0); }

prog.cpp: In function ‘int main()’:
prog.cpp:4:27: error: ‘using type = int’ is protected within this context
 int main() { return base::type(0); }
                           ^~~~
prog.cpp:2:42: note: declared protected here
 struct base { protected: using type = int; };
                                          ^

...
	using BASE::type;
...

...
	using BASE::type;
...

#ifndef USING_SIMPLE_BASE
	#include <tuple>
	#define BASE std::tuple_element_t<0,std::tuple<base<T>>>
#else
	#define BASE base<T>
#endif

template<typename> struct base { protected: using type = int; };

template<typename T> struct derived :private BASE
{
	using type = typename BASE::type;
};

int main() { return derived<int>::type(0); }

struct base
{
  protected:
    using type = int;
};

template< class T >
struct identity
{
    using type_ = T; // (1) work
//    using type  = T; // (2) don't work
};

struct derived : private base
{
  public:
    using typename identity< base >::type_::type; // (1) work

//    using typename identity< base >::type::type;  // (2) don't work
};

int main()
{
	return derived::type();
}