c++ - 为后期初始化转发参数

Question

我正在尝试构建一个通用的 tcp_server 模板，并且我想在创建连接后将一些参数转发给客户端类。然而，客户端对象的创建只发生在他连接之后，而不是在 tcp_server 构建期间。如何将参数从 tcp_server 构造函数传递到客户端构造函数？参数不能复制，只能引用。

下面的代码是我到目前为止建模的代码，但我不确定如何转发客户端对象参数。

template<class client_connection, typename... client_parameters>
class tcp_server
{
private:
    tcp_server(const tcp_server&) = delete;
    tcp_server& operator=(const tcp_server&) = delete;

    boost::asio::io_service& io_service;

    boost::asio::ip::tcp::acceptor acceptor;
    boost::asio::ip::tcp::socket socket;

    void start_accept()
    {
        acceptor.async_accept(socket, [this](const boost::system::error_code& ec)
        {
            if (!ec)
            {
                std::make_shared<client_connection>(io_service, std::move(socket), client_params)->start();
            }

            start_accept();
        });
    }

public:
    tcp_server(boost::asio::io_service& io_service, const std::string& address, const std::string& service, client_parameters&&...client_params)
        :
        io_service(io_service),
        acceptor(io_service),
        socket(io_service)
    {
        boost::asio::ip::tcp::resolver resolver(io_service);
        boost::asio::ip::tcp::resolver::query query(address, service);
        boost::asio::ip::tcp::endpoint endpoint = *resolver.resolve(query);
        acceptor.open(endpoint.protocol());
        acceptor.set_option(boost::asio::ip::tcp::acceptor::reuse_address(true));
        acceptor.bind(endpoint);
        acceptor.listen();

        start_accept();
    }
};

Answer 1

您可以执行以下操作:

template<typename client_connection, typename... client_parameters>
class tcp_server
{
public:

    template <typename... Ts>
    explicit tcp_server(Ts&&... args) : client_params(std::forward<Ts>(args)...) {}

    std::unique_ptr<client_connection> CreateClient()
    {
        return CreateClient(std::index_sequence_for<client_parameters...>{});
    }

private:
    template <std::size_t...Is>
    std::unique_ptr<client_connection> CreateClient(std::index_sequence<Is...>)
    {
        return std::make_unique<client_connection>(std::get<Is>(client_params)...);
    }

private:
    std::tuple<client_parameters...> client_params;
};

然后有类似的东西:

using my_server_t = tcp_server<MyConnection, BigType&, int>;

您在类型中指定哪些参数通过引用或值保存。