#include <coroutine>

#include <iostream>

#include <stdexcept>

#include <thread>

auto switch_to_new_thread(std::jthread& out) {

struct awaitable {

std::jthread* p_out;

bool await_ready() { return false; }

void await_suspend(std::coroutine_handle<> h) {

std::jthread& out = *p_out;

if (out.joinable())

throw std::runtime_error("Output jthread parameter not empty");

out = std::jthread([h] { h.resume(); });

// Potential undefined behavior: accessing potentially destroyed *this

// std::cout << "New thread ID: " << p_out->get_id() << '\n';

std::cout << "New thread ID: " << out.get_id() << '\n'; // this is OK

}

void await_resume() {}

};

return awaitable{&out};

}

struct task{

struct promise_type {

task get_return_object() { return {}; }

std::suspend_never initial_suspend() { return {}; }

std::suspend_never final_suspend() noexcept { return {}; }

void return_void() {}

void unhandled_exception() {}

};

};

task resuming_on_new_thread(std::jthread& out) {

std::cout << "Coroutine started on thread: " << std::this_thread::get_id() << '\n';

co_await switch_to_new_thread(out);

// awaiter destroyed here

std::cout << "Coroutine resumed on thread: " << std::this_thread::get_id() << '\n';

}

int main() {

std::jthread out;

resuming_on_new_thread(out);

}