#include <iostream>
#include <boost/tuple/tuple.hpp>
#include <boost/tuple/tuple_io.hpp>

int main() {

    // OK
    boost::tuple<int> a;

    // OK
    // (0)
    std::cout << a << std::endl;

    // OK
    boost::tuple<> b;

    // compiler error
    // expected: ()
    std::cout << b << std::endl;

}