#ifndef ASYNCIO_RESULT_H
#define ASYNCIO_RESULT_H#include <asyncio/exception.h>
#include <variant>
#include <optional>
namespace ASYNCIO_NS {// 结果类封装（不是协程函数的返回类型）
template<typename T>
struct Result {constexpr bool has_value() const noexcept {return std::get_if<std::monostate>(&result_) == nullptr;}template<typename R>constexpr void set_value(R&& value) noexcept {result_.template emplace<T>(std::forward<R>(value));}template<typename R> // for promise_typeconstexpr void return_value(R&& value) noexcept {return set_value(std::forward<R>(value));}constexpr T result() & {if (auto exception = std::get_if<std::exception_ptr>(&result_)) {std::rethrow_exception(*exception);}if (auto res = std::get_if<T>(&result_)) {return *res;}throw NoResultError{};}constexpr T result() && {if (auto exception = std::get_if<std::exception_ptr>(&result_)) {std::rethrow_exception(*exception);}if (auto res = std::get_if<T>(&result_)) {return std::move(*res);}throw NoResultError{};}void set_exception(std::exception_ptr exception) noexcept { result_ = exception; }void unhandled_exception() noexcept { result_ = std::current_exception(); }private:std::variant<std::monostate, T, std::exception_ptr> result_;
};// 特例化
template<>
struct Result<void> {constexpr bool has_value() const noexcept {return result_.has_value();}void return_void() noexcept {result_.emplace(nullptr);}void result() {if (result_.has_value() && *result_ != nullptr) { std::rethrow_exception(*result_); }}void set_exception(std::exception_ptr exception) noexcept { result_ = exception; }void unhandled_exception() noexcept { result_ = std::current_exception(); }private:std::optional<std::exception_ptr> result_;
};}
#endif // ASYNCIO_RESULT_H