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#include <iostream>
 
template<typename T>
struct to_void
{
	typedef void type;
};
 
class Foo
{
	friend struct Checker;
 
	typedef int TD;
};
 
struct Checker
{
	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 << Checker::has_TD<Foo>::value << std::endl;
}

prog.cpp: In function 'int main()':
prog.cpp:13:14: error: 'typedef int Foo::TD' is private
  typedef int TD;
              ^
prog.cpp:27:33: error: within this context
  std::cout << std::boolalpha << Checker::has_TD<Foo>::value << std::endl;
                                 ^

Standard output is empty