coropromise.hpp

The following code example is taken from the book
C++20 - The Complete Guide by Nicolai M. Josuttis, Leanpub, 2021
The code is licensed under a Creative Commons Attribution 4.0 International License.

---

#include <iostream>
#include <coroutine>
#include <exception>  // for terminate()

// API to control the basic handling of a coroutine
// and to deal with a result or an exception
template<typename CoroType>
struct CoroPromise {
  auto get_return_object() {        // create the coroutine handle
    std::cout << "- promise: get_return_object()\n";
    return std::coroutine_handle<CoroPromise<CoroType>>::from_promise(*this);
  }
  auto initial_suspend() {          // start immediately?
    std::cout << "- promise: initial_suspend()\n";
    return std::suspend_always{};   // - suspend immediately
  }
  auto final_suspend() noexcept {   // clean-ups / postprocessing
    std::cout << "- promise: final_suspend()\n";
    return std::suspend_always{};   // - suspend at the end
  }
  void unhandled_exception() {      // deal with exceptions
    std::terminate();               // - terminate the program
  }
  void return_void() {              // deal with the end or with return;
    std::cout << "- promise: return_void()\n";
  }
};