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template <typename...>
struct Seq;
 
template <typename>
struct always_false
{
	static constexpr bool value = false;
};
 
template <typename, typename = void>
struct car;
 
template <typename head, typename... tail, typename dummy>
struct car<Seq<head, tail...>, dummy>
{
	typedef head type;
};
 
template <typename dummy>
struct car<Seq<>, dummy>
{
	static_assert(always_false<dummy>::value, "car of empty Seq");
};
 
#include <iostream>
#include <typeinfo>
 
int main()
{
	car<Seq<>> error;
}

prog.cpp: In instantiation of ‘struct car<Seq<> >’:
prog.cpp:30:13:   required from here
prog.cpp:22:2: error: static assertion failed: car of empty Seq
  static_assert(always_false<dummy>::value, "car of empty Seq");
  ^
prog.cpp: In function ‘int main()’:
prog.cpp:30:13: warning: unused variable ‘error’ [-Wunused-variable]
  car<Seq<>> error;
             ^

Standard output is empty