Function async_write_messages

example/cpp11/operations/composed_6.cpp:198–253

template <typename T, typename CompletionToken>
auto async_write_messages(tcp::socket& socket,
    const T& message, std::size_t repeat_count,
    CompletionToken&& token)
  // The return type of the initiating function is deduced from the combination
  // of:
  //
  // - the CompletionToken type,
  // - the completion handler signature, and
  // - the asynchronous operation's initiation function object.
  //
  // When the completion token is a simple callback, the return type is always
  // void. In this example, when the completion token is boost::asio::yield_context
  // (used for stackful coroutines) the return type would also be void, as
  // there is no non-error argument to the completion handler. When the
  // completion token is boost::asio::use_future it would be std::future<void>. When
  // the completion token is boost::asio::deferred, the return type differs for each
  // asynchronous operation.
  //
  // In C++11 we deduce the type from the call to boost::asio::async_initiate.
  -> decltype(
      boost::asio::async_initiate<
        CompletionToken, void(boost::system::error_code)>(
          async_write_message_initiation(), token, std::ref(socket),
          std::declval<std::unique_ptr<std::string>>(), repeat_count,
          std::declval<std::unique_ptr<boost::asio::steady_timer>>()))
{
  // Encode the message and copy it into an allocated buffer. The buffer will
  // be maintained for the lifetime of the composed asynchronous operation.
  std::ostringstream os;
  os << message;
  std::unique_ptr<std::string> encoded_message(new std::string(os.str()));

  // Create a steady_timer to be used for the delay between messages.
  std::unique_ptr<boost::asio::steady_timer> delay_timer(
      new boost::asio::steady_timer(socket.get_executor()));

  // The boost::asio::async_initiate function takes:
  //
  // - our initiation function object,
  // - the completion token,
  // - the completion handler signature, and
  // - any additional arguments we need to initiate the operation.
  //
  // It then asks the completion token to create a completion handler (i.e. a
  // callback) with the specified signature, and invoke the initiation function
  // object with this completion handler as well as the additional arguments.
  // The return value of async_initiate is the result of our operation's
  // initiating function.
  //
  // Note that we wrap non-const reference arguments in std::reference_wrapper
  // to prevent incorrect decay-copies of these objects.
  return boost::asio::async_initiate<
    CompletionToken, void(boost::system::error_code)>(
      async_write_message_initiation(), token, std::ref(socket),
      std::move(encoded_message), repeat_count, std::move(delay_timer));
}

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