Append to existing tuple in c++

Question

i am trying to make a thing to store types in list. The best thing is to use a tuple. then to get the type i use tuple_element_t. But the problem is when appending to the tuple so i can store more types. I found that you can append by tuple_cat by this is making a brand new tuple this is problem because i cannot assign it to the one in private section in class and cannot use it in functions inside class. Is there any way to do it?

#include <iostream>
#include <tuple>

using namespace std;

int main() {
    
    auto main_tuple = make_tuple("Hello World");
    auto appended_tuple = tuple_cat(main_tuple,make_tuple(1));
    
    main_tuple = appended_tuple; //How to do this?
    
    return 0;
}

Answer 1

At the point where main_tuple is defined its underlying type is std::tuple<const char*>. The resulting type of appended_tuple in the next line is std::tuple<const char*, int>. Since these two types don't match you can't assign them to each other.

As mentioned in the comments you may want to go for a container of 'wrappers' around your types instead - most prominently std::any or std::variant.

Since you were asking about std::tuple I assume you don't have to perform type-erasure (this is what std::any does), so a possible solution could be the usage of a container like std::vector with std::variant:

#include <string>
#include <variant>
#include <vector>

int main()
{
    using MyVariant = std::variant<int, std::string>;
    using MyVector = std::vector<MyVariant>;

    auto main_vector = MyVector{std::string("Hello World")};
    auto appended_tuple = main_vector;
    appended_tuple.push_back(456);

    return 0;
}

In order now to check for the variant's inner type you can go for functions like get_if, holds_alternative, index... - or write your own visitor that can be applied via std::visit.