std::any::type(3)

NAME
std::any::type - std::any::type

Synopsis
   const std::type_info& type() const noexcept; (since C++17)
   Queries the contained type.

Parameters
   (none)

Return value
   The typeid of the contained value if instance is non-empty, otherwise typeid(void).

Example
   The example demonstrates std::any visitor idiom with ability to register new
   visitors at compile- and run-time. // Run this code
 #include <any>
 #include <functional>
 #include <iomanip>
 #include <iostream>
 #include <type_traits>
 #include <typeindex>
 #include <typeinfo>
 #include <unordered_map>
 #include <vector>
 template<class T, class F>
 inline std::pair<const std::type_index, std::function<void(std::any const&)>>
     to_any_visitor(F const& f)
 {
     return
     {
         std::type_index(typeid(T)),
         [g = f](std::any const& a)
         {
             if constexpr (std::is_void_v<T>)
                 g();
             else
                 g(std::any_cast<T const&>(a));
         }
     };
 }
 static std::unordered_map<std::type_index, std::function<void(std::any const&)>>
     any_visitor
 {
     to_any_visitor<void>([] { std::cout << "{}"; }),
     to_any_visitor<int>([](int x) { std::cout << x; }),
     to_any_visitor<unsigned>([](unsigned x) { std::cout << x; }),
     to_any_visitor<float>([](float x) { std::cout << x; }),
     to_any_visitor<double>([](double x) { std::cout << x; }),
     to_any_visitor<char const*>([](char const* s)
         { std::cout << std::quoted(s); }),
     // ... add more handlers for your types ...
 };
 inline void process(const std::any& a)
 {
     if (const auto it = any_visitor.find(std::type_index(a.type()));
         it != any_visitor.cend())
         it->second(a);
     else
         std::cout << "Unregistered type "<< std::quoted(a.type().name());
 }
 template<class T, class F>
 inline void register_any_visitor(F const& f)
 {
     std::cout << "Register visitor for type "
               << std::quoted(typeid(T).name()) << '\n';
     any_visitor.insert(to_any_visitor<T>(f));
 }
 int main()
 {
     std::vector<std::any> va{{}, 42, 123u, 3.14159f, 2.71828, "C++17"};
     std::cout << "{ ";
     for (const std::any& a : va)
     {
         process(a);
         std::cout << ", ";
     }
     std::cout << "}\n";
     process(std::any(0xFULL)); //< Unregistered type "y" (unsigned long long)
     std::cout << '\n';
     register_any_visitor<unsigned long long>([](auto x)
     {
         std::cout << std::hex << std::showbase << x;
     });
     process(std::any(0xFULL)); //< OK: 0xf
     std::cout << '\n';
 }

Possible output:
 { {}, 42, 123, 3.14159, 2.71828, "C++17", }
 Unregistered type "y"
 Register visitor for type "y"
 0xf

See also
   type_index wrapper around a type_info object, that can be used as index in
   (C++11) associative and unordered associative containers
              (class)