[section:history Revision History]
+[heading Asio 1.16.0 / Boost 1.72]
+
+* Changed the `async_initiate` helper function to automatically deduce its
+ return type. This is enabled for C++11 or later.
+* Changed all asynchronous operations to use automatically deduced return
+ types. This allows completion token implementations to incorporate the
+ asynchronous operation initiation into the initiating function's return type,
+ without type erasure. Note that C++14 or later is required to support
+ completion tokens that use per-operation return type deduction. For C++11 or
+ earlier, a completion token's async_result specialisation must still provide
+ the nested typedef `return_type`.
+* Introduced three new concepts to support `async_initiate`.
+ * `completion_signature<T>`: Checks if `T` is a signature of the form
+ `R(Args...)`.
+ * `completion_handler_for<T, Signature>`: Checks if `T` is usable as a
+ completion handler with the specified signature.
+ * `completion_token_for<T, Signature>`: Checks if `T` is a completion token
+ that can be used with async_initiate and the specified signature.
+ * For backward compatibility with pre-concepts C++, the macros
+ `BOOST_ASIO_COMPLETION_SIGNATURE`, `BOOST_ASIO_COMPLETION_HANDLER_FOR`, and
+ `BOOST_ASIO_COMPLETION_TOKEN_FOR` are provided. These macros expand to
+ `typename` when concepts are unsupported.
+* Added the nested template type `rebind_executor` to all I/O object types, as
+ a way to generically rebind them to use alternative I/O executors. For
+ example:
+ ``
+ using my_socket_type = tcp::socket::rebind_executor<my_executor_type>::other;
+ ``[br]
+* Changed the asynchronous operations' initiation function objects to report
+ their associated I/O executor via the nested type `executor_type` and member
+ function `get_executor()`. Note that the presence of `executor_type` and
+ `get_executor()` should be treated as optional, and consequently it may be
+ preferable to access them via the `associated_executor` trait and the
+ `get_associated_executor()` helper function.
+* Added the `default_completion_token` trait, so that every I/O executor type
+ now has an associated default completion token type. This trait may be used
+ in asynchronous operation declarations as follows:
+ ``
+ template <
+ typename IoObject,
+ typename CompletionToken =
+ typename default_completion_token<
+ typename IoObject::executor_type
+ >::type
+ >
+ auto async_fyz(
+ IoObject& io_object,
+ CompletionToken&& token =
+ typename default_completion_token<
+ typename IoObject::executor_type
+ >::type{}
+ );
+ ``[br]
+ If not specialised, this trait type is `void`, meaning no default completion
+ token type is available for the given I/O executor.
+* Specialised the `default_completion_token` trait for the `use_awaitable`
+ completion token, so that it may be used as shown in the following example:
+ ``
+ auto socket = use_awaitable.as_default_on(tcp::socket(my_context));
+ // ...
+ co_await socket.async_connect(my_endpoint); // Defaults to use_awaitable.
+ ``[br]
+ In this example, the type of the `socket` object is transformed from
+ `tcp::socket` to have an I/O executor with the default completion token set
+ to `use_awaitable`. Alternatively, the socket type may be computed directly:
+ ``
+ using tcp_socket = use_awaitable_t<>::as_default_on_t<tcp::socket>;
+ tcp_socket socket(my_context);
+ // ...
+ co_await socket.async_connect(my_endpoint); // Defaults to use_awaitable.
+ ``[br]
+* Added missing `async_initiate` to the Windows-specific I/O objects'
+ asynchronous operations.
+* Ensured that the executor type is propagated to newly accepted sockets.
+ When synchronously or asynchronously accepting a new connection, but
+ without specifying an executor or execution context, the accept
+ operation will now correctly propagate the executor type from the
+ acceptor to the socket. For example, if your acceptor type is:
+ ``
+ basic_socket_acceptor<ip::tcp, my_executor_type>
+ ``[br]
+ then your accepted socket type will be:
+ ``
+ basic_stream_socket<ip::tcp, my_executor_type>
+ ``[br]
+* Changed to require that `Protocol` copy and move operations never throw.
+* Changed to require that `Endpoint` default constructor and move operations
+ never throw.
+* Added the `noexcept` qualifier to protocol accessors.
+* Added the `noexcept` qualifier to socket move constructors.
+* Fixed issues associated with opening serial ports on Windows:
+ * Use the correct constant to initialise the RTS control flag.
+ * Specify a default baud rate (9600).
+* Fixed a lost "outstanding work count" that can occur when an asynchronous
+ accept operation is automatically restarted.
+
[heading Asio 1.14.1 / Boost 1.71]
* Improved performance slightly by eliminating a redundant move construction
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