ASIO/Networking TS : Boost < 1.70

  // Dynamically allocate a buffer to read into. This must be move-only
  // so it can be attached to the completion handler, hence the unique_ptr.
  auto buffer = std::make_unique<std::vector<byte>>(1024);

  // Begin an asynchronous socket read, upon completion invoke
  // the lambda function specified
  skt.async_read_some(asio::buffer(buffer->data(), buffer->size()),

                      // Retain lifetime of the i/o buffer until completion
                      [buffer = std::move(buffer)](const error_code &ec, size_t bytes) {
                        // Handle the buffer read
                        if(ec)
                        {
                          std::cerr << "Buffer read failed with " << ec << std::endl;
                          return;
                        }
                        std::cout << "Read " << bytes << " bytes into buffer" << std::endl;

                        // buffer will be dynamically freed now
                      });

  // As coroutines suspend the calling thread whilst an asynchronous
  // operation executes, we can use stack allocation instead of dynamic
  // allocation
  char buffer[1024];

  // Get an ASIO completion token for the current coroutine (requires
  // Coroutines TS)
  asio::experimental::await_token token =  //
  co_await asio::experimental::this_coro::token();

  // Asynchronously read data, suspending this coroutine until completion,
  // returning the bytes of the data read into the result.
  try
  {
    size_t bytesread =  //
    co_await skt.async_read_some(asio::buffer(buffer), token);
    std::cout << "Read " << bytesread << " bytes into buffer" << std::endl;
  }
  catch(const std::system_error &e)
  {
    std::cerr << "Buffer read failed with " << e.what() << std::endl;
  }

  // Asynchronously read data, suspending this coroutine until completion,
  // returning the bytes of the data read into the result, or any failure.
  outcome::result<size_t, error_code> bytesread =  //
  co_await skt.async_read_some(asio::buffer(buffer), as_result(token));

  // Usage is exactly like ordinary Outcome. Note the lack of exception throw!
  if(bytesread.has_error())
  {
    std::cerr << "Buffer read failed with " << bytesread.error() << std::endl;
    return;
  }
  std::cout << "Read " << bytesread.value() << " bytes into buffer" << std::endl;

namespace detail
{
  // Type sugar for wrapping an external completion token
  template <class CompletionToken> struct as_result_t
  {
    CompletionToken token;
  };
}  // namespace detail

// Factory function for wrapping a third party completion token with
// our type sugar
template <class CompletionToken>  //
inline auto as_result(CompletionToken &&token)
{
  return detail::as_result_t<std::decay_t<CompletionToken>>{std::forward<CompletionToken>(token)};
};

// Tell ASIO about a new kind of completion token, the kind returned
// from our as_result() factory function. This implementation is
// for functions with handlers void(error_code, T) only.
template <class CompletionToken, class T>                        //
struct asio::async_result<detail::as_result_t<CompletionToken>,  //
                          void(error_code, T)>                   //

    // NOTE we subclass for an async result taking an outcome::result
    // as its completion handler. We will mangle the void(error_code, T)
    // completion handler into this completion handler below.
    : public asio::async_result<CompletionToken, void(outcome::result<T, error_code>)>
{
  // The result type we shall return
  using result_type = outcome::result<T, error_code>;
  using _base = asio::async_result<CompletionToken, void(result_type)>;
  // The awaitable type to be returned by the initiating function,
  // the co_await of which will yield a result_type
  using return_type = typename _base::return_type;

  // Get what would be the completion handler for the async_result
  // whose completion handler is void(result_type)
  using result_type_completion_handler_type =  //
  typename _base::completion_handler_type;

  // Wrap that completion handler with void(error_code, T) converting
  // handler
  struct completion_handler_type
  {
    // Pass through unwrapped completion token
    template <class U>
    completion_handler_type(::detail::as_result_t<U> &&ch)
        : _handler(std::forward<U>(ch.token))
    {
    }

    // Our completion handler spec
    void operator()(error_code ec, T v)
    {
      // Call the underlying completion handler, whose
      // completion function is void(result_type)
      if(ec)
      {
        // Complete with a failed result
        _handler(result_type(outcome::failure(ec)));
        return;
      }
      // Complete with a successful result
      _handler(result_type(outcome::success(v)));
    }

    result_type_completion_handler_type _handler;
  };

  // Initialise base with the underlying completion handler
  async_result(completion_handler_type &h)
      : _base(h._handler)
  {
  }

  using _base::get;
};