Uses allocator construction issue with perfect forwarding

main.cpp

using namespace std;

template<class T1, class T2>
void join(T1&& t1, T2&& t2)
{
	static_assert(is_same<decltype(get<0>(t1)), int&&>::value); // fails
}

template<class T1, class T2>
auto foward_pair(pair<T1, T2>&& p)
{
	static_assert(is_same<T1, int&&>::value);
	return join(forward_as_tuple(move(p).first),
		        forward_as_tuple(move(p).second));
}

int main()
{
	int x = 42;
	pair<int&&, int&&> p = make_pair(std::move(x), std::move(x));
	foward_pair(move(p));
}

Ignore the spacing. Github won't let me change it.