#include <type_traits>
#include <any>
#include <functional>
#include <iomanip>
#include <iostream>
#include <typeindex>
#include <typeinfo>
#include <unordered_map>
#include <vector>
//any是編譯期的異質集合，要顯示指定處理的類型；我們可以記錄每種類型的哈希值，實現運行期動態處理這樣的異質集合
//這里我們根據類型信息的哈希值去bind每種類型的處理函數//綁定器生成器
template<class T, class F>
inline std::pair<const std::type_index, std::function<void(std::any const&)>>
GeneratorBinder(F const& f)
{return {std::type_index(typeid(T)),[g = f](std::any const& a){if constexpr (std::is_void_v<T>)g();elseg(std::any_cast<T const&>(a));}};
}
//定義綁定器集合
static std::unordered_map<std::type_index, std::function<void(std::any const&)>> any_visitor
{//注冊基本類型的處理函數GeneratorBinder<void>([] { std::cout << "{}"; }),GeneratorBinder<int>([](int x) { std::cout << x; }),GeneratorBinder<unsigned>([](unsigned x) { std::cout << x; }),GeneratorBinder<float>([](float x) { std::cout << x; }),GeneratorBinder<double>([](double x) { std::cout << x; }),GeneratorBinder<char const*>([](char const* s){ std::cout << std::quoted(s);})
};
//處理器
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());}
}//注冊器
template<class T, class F>
inline void registrar(F const& f)
{std::cout << "Register visitor for type "<< std::quoted(typeid(T).name()) << '\n';any_visitor.insert(to_any_visitor<T>(f));
}auto main() -> int
{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)); //未注冊的類型std::cout << '\n';//注冊操作registrar<unsigned long long>([](auto x) {std::cout << std::hex << std::showbase << x;});process(std::any(0xFULL)); //< OK ： 0xfstd::cout << '\n';return 0;
}