C++ tuple输出

// c++11
template<typename Tuple, size_t N>
struct tuple_print {
   static void print(const Tuple& t, std::ostream& os) {
       tuple_print<Tuple, N - 1>::print(t, os);
       os << ", " << std::get<N - 1>(t);
   }
};
// 类模板的特化版本
template<typename Tuple>
struct tuple_print<Tuple, 1> {
   static void print(const Tuple& t, std::ostream& os) {
       os << "(" << std::get<0>(t);
   }
};

// operator<<
template<typename... Args>
std::ostream& operator <<(std::ostream& os, const std::tuple<Args...>& t) {
   tuple_print<decltype(t), sizeof...(Args)>::print(t, os);
   return os << ")";
}

//C++14
// 数组转换为 tuple
template<typename Array, std::size_t... I>
auto a2t_impl(const Array& a, std::index_sequence<I...>) {
    return std::make_tuple(a[I]...);
}

template<typename T, std::size_t N, typename Indices = std::make_index_sequence<N>>
auto a2t(const std::array<T, N>& a) {
    return a2t_impl(a, Indices{});
}

// 漂亮地打印 tuple

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 << ")";
}

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