Christopher Kohlhoff f486b43c16 Add operator&& and operator|| for awaitable<>. ...

The logical operators || and && have been overloaded for awaitable<>, to
allow coroutines to be trivially awaited in parallel.

When awaited using &&, the await expression waits until both operations
have completed successfully. As a "short-circuit" evaluation, if one
operation fails with an exception, the other is immediately cancelled.
For example:

    std::tuple<std::size_t, std::size_t> results =
      co_await (
        async_read(socket, input_buffer, use_awaitable)
          && async_write(socket, output_buffer, use_awaitable)
      );

When awaited using ||, the await expression waits until either operation
succceeds. As a "short-circuit" evaluation, if one operation succeeds
without throwing an exception, the other is immediately cancelled. For
example:

    std::variant<std::size_t, std::monostate> results =
      co_await (
        async_read(socket, input_buffer, use_awaitable)
          || timer.async_wait(use_awaitable)
      );

The operators may be enabled by adding the #include:

    #include <asio/experimental/awaitable_operators.hpp>

and then bringing the contents of the experimental::awaitable_operators
namespace into scope:

    using namespace boost::asio::experimental::awaitable_operators;

2021-07-04 13:05:46 +10:00

..

asio

Add operator&& and operator|| for awaitable<>.

2021-07-04 13:05:46 +10:00

asio.hpp

Add cancellation_state.

2021-06-28 10:10:27 +10:00