boost::hana::map as a data member - c++

Question

I am currently learning boost::hana for a personal project.
In the following code snippet I created a boost::hana::map having a type_c<T> as key and an instance of Foo<T> as value.
It works but I would really like to use the my_map variable as a class member and it is not possible to use auto qualifier in member declarations. Moreover it would be great if I could have the possibility to pass the types tuple in some way (as a template parameter or as a constructor parameter).
Do you have any suggestions?
#include <iostream>
#include "boost/hana.hpp"
#include <typeinfo>
using namespace boost;
template<typename T>
class Foo {
T t;
public:
void print() { std::cout <<typeid(T).name() << t; }
};
int main() {
auto types = hana::tuple_t<float, int, std::string>;
auto my_map = boost::hana::unpack(types, [](auto ...t) {
return boost::hana::make_map(boost::hana::make_pair(t, Foo<typename decltype(t)::type>()) ...);
});
my_map[hana::type_c<int>].print();
}

Answer 1

The problem is that lambdas cannot be used in un-evaluated context (decltype).
Of course, since c++14 we can just use deduced return types on any free function:
namespace detail {
template <typename... T>
static inline auto make_foo_map() {
return boost::hana::unpack(hana::tuple_t<T...>, [](auto... t) {
return boost::hana::make_map(boost::hana::make_pair(t, Foo<typename decltype(t)::type>())...);
});
}
}
template <typename... T>
using FooMap = decltype(detail::make_foo_map<T...>());
Now it's simply:
FooMap<float, int, std::string> my_map;
Live Demo
Live On Coliru
#include "boost/hana.hpp"
#include <iostream>
#include <typeinfo>
using namespace boost;
template <typename T> class Foo {
T t;
public:
void print() { std::cout << typeid(T).name() << "t\n"; }
};
namespace detail {
template <typename... T>
static inline auto make_foo_map() {
return boost::hana::unpack(hana::tuple_t<T...>, [](auto... t) {
return boost::hana::make_map(boost::hana::make_pair(t, Foo<typename decltype(t)::type>())...);
});
}
}
template <typename... T>
using FooMap = decltype(detail::make_foo_map<T...>());
int main() {
FooMap<float, int, std::string> my_map;
my_map[hana::type_c<int>].print();
my_map[hana::type_c<float>].print();
my_map[hana::type_c<std::string>].print();
}