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. Creative Commons License

// raw code

template<typename Hdl>
class BackAwaiter {
  Hdl hdl = nullptr;   // coroutine handle saved from await_suspend() for await_resume()
  BackAwaiter() = default;

  bool await_ready() const noexcept {
    return false;                    // do suspend

  void await_suspend(Hdl h) noexcept {
    hdl = h;                         // save handle to get access to its promise

  auto await_resume() const noexcept {
    return hdl.promise().backValue;  // return back value stored in the promise