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#include <iostream>
 
template<typename T>
struct to_void
{
	typedef void type;
};
 
class Foo
{
	typedef int TD;
};
 
template <typename T, typename dummy = void>
struct has_TD : std::false_type {};
 
template <typename T>
struct has_TD<T, typename to_void<typename T::TD>::type > : std::true_type{};
 
int main()
{
	std::cout << std::boolalpha << has_TD<Foo>::value << std::endl;
}

prog.cpp: In instantiation of 'struct has_TD<Foo>':
prog.cpp:22:44:   required from here
prog.cpp:11:14: error: 'typedef int Foo::TD' is private
  typedef int TD;
              ^
prog.cpp:18:75: error: within this context
 struct has_TD<T, typename to_void<typename T::TD>::type > : std::true_type{};
                                                                           ^
prog.cpp:11:14: error: 'typedef int Foo::TD' is private
  typedef int TD;
              ^
prog.cpp:18:75: error: within this context
 struct has_TD<T, typename to_void<typename T::TD>::type > : std::true_type{};
                                                                           ^
prog.cpp: In function 'int main()':
prog.cpp:11:14: error: 'typedef int Foo::TD' is private
  typedef int TD;
              ^
prog.cpp:22:33: error: within this context
  std::cout << std::boolalpha << has_TD<Foo>::value << std::endl;
                                 ^

Standard output is empty