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#pragma once
#include <coroutine>
#include <optional>
namespace aisa {
template<typename result_t> struct task_promise;
template<typename result_t> struct task : public std::coroutine_handle<task_promise<result_t>> {
using handle = std::coroutine_handle<task_promise<result_t>>;
using promise_type = task_promise<result_t>;
bool await_ready() const noexcept { return handle::done(); }
result_t await_resume() const noexcept;
template<typename other_t> void await_suspend(std::coroutine_handle<task_promise<other_t>> h) const noexcept;
std::optional<result_t> operator()() noexcept;
};
template<> struct task<void> : public std::coroutine_handle<task_promise<void>> {
using handle = std::coroutine_handle<task_promise<void>>;
using promise_type = task_promise<void>;
bool await_ready() const noexcept { return handle::done(); }
void await_resume() const noexcept;
template<typename other_t> void await_suspend(std::coroutine_handle<task_promise<other_t>> h) const noexcept;
bool operator()() noexcept;
};
template<typename result_t> struct task_promise {
std::coroutine_handle<> precursor;
std::optional<result_t> result;
task_promise() = default;
task_promise(const task_promise &) = delete;
task<result_t> get_return_object() noexcept { return task<result_t>{std::coroutine_handle<task_promise<result_t>>::from_promise(*this)}; }
std::suspend_never initial_suspend() const noexcept { return {}; }
std::suspend_always final_suspend() const noexcept { return {}; }
void unhandled_exception() { }
void return_value(result_t x) noexcept { result = std::move(x); }
};
template<> struct task_promise<void> {
std::coroutine_handle<> precursor;
task_promise() = default;
task_promise(const task_promise &) = delete;
task<void> get_return_object() noexcept { return task<void>{std::coroutine_handle<task_promise<void>>::from_promise(*this)}; }
std::suspend_never initial_suspend() const noexcept { return {}; }
std::suspend_always final_suspend() const noexcept { return {}; }
void unhandled_exception() { }
void return_void() noexcept { }
};
template<typename result_t> result_t task<result_t>::await_resume() const noexcept
{
auto x = std::move(handle::promise().result.value());
handle::destroy();
return x;
}
template<typename result_t> template<typename other_t> void task<result_t>::await_suspend(std::coroutine_handle<task_promise<other_t>> h) const noexcept
{
h.promise().precursor = *this;
}
template<typename result_t> std::optional<result_t> task<result_t>::operator()() noexcept
{
if (!handle::operator bool())
return {};
if (!handle::done()) {
auto &precursor = handle::promise().precursor;
if (precursor) {
if (!precursor.done())
precursor.resume();
if (precursor.done())
precursor = nullptr;
}
if (!precursor)
handle::resume();
}
if (handle::done()) {
auto x = await_resume();
handle::operator=(nullptr);
return x;
}
return {};
}
inline void task<void>::await_resume() const noexcept
{
handle::destroy();
}
template<typename other_t> void task<void>::await_suspend(std::coroutine_handle<task_promise<other_t>> h) const noexcept
{
h.promise().precursor = *this;
}
inline bool task<void>::operator()() noexcept
{
if (!handle::operator bool())
return true;
if (!handle::done()) {
auto &precursor = handle::promise().precursor;
if (precursor) {
if (!precursor.done())
precursor.resume();
if (precursor.done())
precursor = nullptr;
}
if (!precursor)
handle::resume();
}
if (handle::done()) {
await_resume();
handle::operator=(nullptr);
return true;
}
return false;
}
}
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