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use variant like julia union
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| #include <iostream> | |
| #include <random> | |
| #include <type_traits> | |
| #include <variant> | |
| template <class T> struct replace_void { using type = T; }; | |
| template <> struct replace_void<void> { using type = std::monostate; }; | |
| template <class T> using replace_void_t = typename replace_void<T>::type; | |
| template <class... Fn> struct overloaded : Fn... { | |
| using Fn::operator()...; | |
| template <class... T> | |
| auto operator()(std::variant<std::monostate, T...> arg) { | |
| using Res = | |
| std::variant<std::monostate, | |
| replace_void_t<std::invoke_result_t<overloaded, T>>...>; | |
| auto res = Res(); | |
| auto try_set = [&]<class S>() { | |
| using R = std::invoke_result_t<overloaded, S>; | |
| if constexpr (std::is_void_v<R>) { | |
| this->operator()(std::get<S>(arg)); | |
| } else { | |
| res = Res(this->operator()(std::get<S>(arg))); | |
| } | |
| return true; | |
| }; | |
| ((std::holds_alternative<T>(arg) && try_set.template operator()<T>()), ...); | |
| return res; | |
| } | |
| }; | |
| template <class... Fn> overloaded(Fn...)->overloaded<Fn...>; | |
| int main() { | |
| auto e = std::default_random_engine(std::random_device()()); | |
| auto d = std::uniform_real_distribution<double>(0, 1); | |
| using tp = std::variant<std::monostate, double, int>; | |
| auto p = tp(); | |
| if (auto v = d(e); v > 0.5) { | |
| p = v; | |
| } else { | |
| p = static_cast<int>(v * 1000); | |
| } | |
| auto f = | |
| overloaded{[](int p) { std::cout << "v :: int = " << p << "\n"; return double(p);}, | |
| [](double p) { std::cout << "v :: double = " << p << "\n"; return int(p*1000);}}; | |
| auto g = | |
| overloaded{[](int p) { std::cout << "w :: int = " << p << "\n"; }, | |
| [](double p) { std::cout << "w :: double = " << p << "\n"; }}; | |
| g(f(p)); | |
| return 0; | |
| } |
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| function f(p::Int64) | |
| print("v :: int = $p\n"); | |
| return Float64(p); | |
| end | |
| function f(p::Float64) | |
| print("v :: double = $p\n"); | |
| return Int64(floor(p*1000)); | |
| end | |
| function g(p::Int64) | |
| print("w :: int = $p\n"); | |
| end | |
| function g(p::Float64) | |
| print("w :: double = $p\n"); | |
| end | |
| p = rand() | |
| if p < 0.5 | |
| p = Int64(floor(p*1000)) | |
| end | |
| g(f(p)) |
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