Christopher Kohlhoff 63972a52c0 Add completion_signature_of trait. ...

The completion_signature_of trait (and corresponding type alias
completion_signature_of_t) may be used to determine the completion
signature of an asynchronous operation. For example:

  auto d = my_timer.async_wait(asio::deferred);
  using sig = asio::completion_signature_of<decltype(d)>::type;
  // sig is void(error_code)

or with a handcrafted asynchronous operation:

  struct my_async_op
  {
    asio::ip::tcp::socket& socket_ = ...;

    template <typename Token>
    auto operator()(asio::const_buffer data, Token&& token)
    {
      return asio::async_write(socket_, data,
          std::forward<Token>(token));
    }
  };

  using sig =
    asio::completion_signature_of<
      my_async_op, asio::const_buffer>::type;
  // sig is void(error_code, size_t)

2022-06-30 01:08:13 +10:00

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