A way for iterate over complex tuple elements

main.cpp

#include <tuple>
#include <vector>
#include <iostream>
#include <utility>
    
template <typename ...Types>
struct A
{    
    std::tuple<std::vector<Types>...> t;
};

namespace detail {
    template<typename T>
    std::string type_str();
    
    template<>
    std::string type_str<int>()
    {
        return std::string{ "int: " };
    }
    
    template<>
    std::string type_str<double>()
    {
        return std::string{ "double: " };
    }
    
    template<>
    std::string type_str<std::string>()
    {
        return std::string{ "string: " };
    }   
}

struct B
{
    
    template<size_t Idx, typename ...Types>
    void print_a(std::integral_constant<bool, true>, std::tuple<std::vector<Types>...> & t)
    {
        using currentTupleType  = typename std::tuple_element<Idx, std::decay_t<decltype(t)>>::type;
        using currentVectorType = typename currentTupleType::value_type;
        
        for(auto && v : std::get<Idx>(t))
        {
            std::cout << detail::type_str<currentVectorType>() << v << std::endl;
        }
    }
    
    template<size_t Idx, typename ...Types>
    void print_a(std::integral_constant<bool, false>, std::tuple<std::vector<Types>...> & t)
    {
        using currentTupleType  = typename std::tuple_element<Idx, std::decay_t<decltype(t)>>::type;
        using currentVectorType = typename currentTupleType::value_type;
        
        for(auto && v : std::get<Idx>(t))
        {
            std::cout << detail::type_str<currentVectorType>() << v << std::endl;
        }
        
        const size_t step_index = Idx - 1;
        print_a<step_index, Types...>( std::integral_constant<bool, step_index == 0>{}, t);
    }
    
    template <typename ...Types>
    void print_a(A<Types...> & a)
    {
        const size_t start_index = std::tuple_size<decltype(a.t)>::value -1;
        print_a<start_index, Types...>( std::integral_constant<bool, start_index == 0>{}, a.t);
    }
    
};

int main()
{
    
    A<int, double, std::string> a;
    std::get<0>(a.t).push_back(1);
    std::get<0>(a.t).push_back(2);
    std::get<1>(a.t).push_back(1.1);
    std::get<1>(a.t).push_back(2.2);
    std::get<2>(a.t).push_back("1 str");
    std::get<2>(a.t).push_back("2 str");
    
    B b;
    b.print_a<int, double, std::string>(a);
    
    return 0;
}