C++14 Compatible Tuple Operator Broadcast

gistfile1.txt

#include <tuple>
#include <utility>

namespace internal
{
    template<typename T, typename T2, size_t... Is>
    void add_rhs_to_lhs(T& t1, const T2& t2, std::integer_sequence<size_t, Is...>)
    {
        auto l = { (std::get<Is>(t1) += std::get<Is>(t2), 0)... };
        (void)l;
        
    }

}

template <typename...T, typename...T2>
std::tuple<T...>& operator += (std::tuple<T...>& lhs, const std::tuple<T2...>& rhs)
{
    internal::add_rhs_to_lhs(lhs, rhs, std::index_sequence_for<T...>{});
    return lhs;
}

template <typename...T>
std::tuple<T...>& operator += (std::tuple<T...>& lhs, const std::tuple<T...>& rhs)
{
    internal::add_rhs_to_lhs(lhs, rhs, std::index_sequence_for<T...>{});
    return lhs;
}


template <typename...T, typename...T2>
std::tuple<T...> operator + (std::tuple<T...> lhs, const std::tuple<T2...>& rhs)
{
   return lhs += rhs;
}

template <typename...T>
std::tuple<T...> operator + (std::tuple<T...> lhs, const std::tuple<T...>& rhs)
{
   return lhs += rhs;
}

#include <iostream>

// see: http://en.cppreference.com/w/cpp/utility/integer_sequence
template<class Ch, class Tr, class Tuple, std::size_t... Is>
void print_tuple_impl(std::basic_ostream<Ch,Tr>& os,
                      const Tuple& t,
                      std::index_sequence<Is...>)
{
    ((os << (Is == 0? "" : ", ") << std::get<Is>(t)), ...);
}

template<class Ch, class Tr, class... Args>
auto& operator<<(std::basic_ostream<Ch, Tr>& os,
                 const std::tuple<Args...>& t)
{
    os << "(";
    print_tuple_impl(os, t, std::index_sequence_for<Args...>{});
    return os << ")";
}

int main()
{
    std::tuple<int,int> a = {1,2};
    std::tuple<int,int> b = {2,4};
    
    std::cout << "a = " << a << '\n';
    std::cout << "b = " << b << '\n';

    std::tuple<int,int> c = a + b; // possible syntax 1
    std::cout << "c = " << c << '\n';
    
    a += b; // possible syntax 2
    std::cout << "a = " << a << '\n';
    
    a += std::make_tuple(3,4); // possible syntax 3
    std::cout << "a = " << a << '\n';
    
    a += {3, 4}; // possible syntax 3
    std::cout << "a = " << a << '\n';
    
    int x = 0;
    int y = 0;
    auto r = std::tie(x, y);
    
    std::cout << "pre: " << x << "\n";    
    r += a;
    
    std::cout << "post: " << x << "\n";

    return 0;
}