c++ - 如何通过我自己的函数传递boost::asio::yield_context？

Question

给一个协程生成..

void my_coroutine(asio::yield_context yield) {
    system::error_code ec;
    my_wrapper(yield[ec]);
    if (ec) {
        // something went wrong
        return;
    }
    ...
}

void my_wrapper(asio::yield_context&& yield) {
    asio::async_read(..., yield);  // any asio async call
    if (ec) {
        // something went wrong
        return;
    }
    ...
}

在包装函数中，无法从传递的yield上下文访问ec。那么如何解决呢？

Answer 1

您想/ oji /使用ec做什么？您可以访问的方式与my_coroutine已经显示的方式完全相同:

void my_wrapper(asio::yield_context&& yield) {
    system::error_code ec;
    asio::async_read(..., yield[ec]);  // any asio async call
    if (ec) {
        // something went wrong
        return;
    }
    ...
}

如果您表示要进行可组合的异步操作，请参见以下模式:

How to set error_code to asio::yield_context

基本示例:

template <typename Token>
auto async_meaning_of_life(bool success, Token&& token)
{
#if BOOST_VERSION >= 106600
    using result_type = typename asio::async_result<std::decay_t<Token>, void(error_code, int)>;
    typename result_type::completion_handler_type handler(std::forward<Token>(token));

    result_type result(handler);
#else
    typename asio::handler_type<Token, void(error_code, int)>::type
                 handler(std::forward<Token>(token));

    asio::async_result<decltype (handler)> result (handler);
#endif

    if (success)
        handler(error_code{}, 42);
    else
        handler(asio::error::operation_aborted, 0);

    return result.get ();
}