EightBit/inc/co_generator_t.h

76 lines
1.9 KiB
C++

#pragma once
#include <coroutine>
#include <utility>
// from https://www.scs.stanford.edu/~dm/blog/c++-coroutines.html
namespace EightBit {
template<typename T>
class co_generator_t final {
public:
class promise_type;
private:
using handle_t = std::coroutine_handle<promise_type>;
class promise_type final {
private:
T value_;
std::exception_ptr exception_;
public:
template<std::convertible_to<T> From> // C++20 concept
[[nodiscard]] constexpr std::suspend_always yield_value(From&& from) noexcept {
value_ = std::forward<From>(from);
return {};
}
[[nodiscard]] constexpr std::suspend_always initial_suspend() noexcept { return {}; }
[[nodiscard]] constexpr std::suspend_always final_suspend() noexcept { return {}; }
[[nodiscard]] constexpr co_generator_t get_return_object() noexcept {
return co_generator_t(handle_t::from_promise(*this));
}
constexpr void return_void() {}
constexpr void unhandled_exception() noexcept { exception_ = std::current_exception(); }
[[nodiscard]] constexpr auto& value() noexcept { return value_; };
[[nodiscard]] constexpr auto& exception() noexcept { return exception_; };
};
handle_t h_;
private:
bool full_ = false;
constexpr void fill() {
if (!full_) {
h_();
if (h_.promise().exception())
std::rethrow_exception(h_.promise().exception());
full_ = true;
}
}
public:
co_generator_t(handle_t h) noexcept : h_(h) {}
~co_generator_t() noexcept { h_.destroy(); }
constexpr explicit operator bool() {
fill();
return !h_.done();
}
[[nodiscard]] constexpr T operator()() {
fill();
full_ = false;
return std::move(h_.promise().value());
}
};
}