код:

---

#include <tuple>
#include <iostream>
 
template<typename T>
class Field
{
    T value_;
public:
    Field(const T& value) : value_(value) {}
    const T& get() const { return value_; }
};
 
template<typename... Fields>
class Message : public std::tuple<Fields...>
{
public:
    Message() : std::tuple<Fields...>() {}
    Message(const Fields&... fields) : std::tuple<Fields...>(fields...) {}
 
    template<typename... UFields>
    Message(UFields&&... fields)
        : std::tuple<Fields...>(std::forward<UFields>(fields)...) {}
 
    template<std::size_t index>
    const Field<typename std::tuple_element<index, std::tuple<Fields...>>::type>
    get() const { return std::get<index>(*this); }
};
 
int main()
{
    Message<int, std::string, int> msg = { 42, "Answer", 21 };
    std::cout << msg.get<0>().get() << "\n";
    std::cout << msg.get<1>().get() << "\n";
    std::cout << msg.get<2>().get() << "\n";
}

---