Function start

examples/algorithms/retry.hpp:83–118

// re-construct and re-start it if the operation fails.
template <class S, class R>
struct _op
{
  S                                                                   s_;
  R                                                                   r_;
  std::optional<stdexec::connect_result_t<S&, _retry_receiver<S, R>>> o_;

  _op(S s, R r)
    : s_(static_cast<S&&>(s))
    , r_(static_cast<R&&>(r))
    , o_{_connect()}
  {}

  _op(_op&&) = delete;

  auto _connect() noexcept
  {
    return _conv{[this] { return stdexec::connect(s_, _retry_receiver<S, R>{this}); }};
  }

  void _retry() noexcept
  {
    STDEXEC_TRY
    {
      o_.emplace(_connect());  // potentially throwing
      stdexec::start(*o_);
    }
    STDEXEC_CATCH_ALL
    {
      stdexec::set_error(static_cast<R&&>(r_), std::current_exception());
    }
  }

  void start() & noexcept
  {
    stdexec::start(*o_);
  }
};

template <class S>