Christopher Kohlhoff 8e0762de49 Add default completion tokens. ... Every I/O executor type now has an associated default completion token type. This is specified via the `default_completion_token_type` trait. This trait may be used in asynchronous operation declarations as follows: template < typename IoObject, typename CompletionToken = typename default_completion_token_type< typename IoObject::executor_type >::type > auto async_foo( IoObject& io_object, CompletionToken&& token = typename default_completion_token_type< typename IoObject::executor_type >::type{} ); If not specialised, this trait type is `void`, meaning no default completion token type is available for the given I/O executor. The `default_completion_token_type` trait is specialised 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. In this example, 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.		2019-10-30 20:51:58 +11:00
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coroutines_ts	Add default completion tokens.	2019-10-30 20:51:58 +11:00