I haven't tested it, but this should probably work: class session { public: session(tcp::socket socket) : session(std::make_unique<session_impl>(std::move(socket))) {} void start() { do_read(); } private: session(std::unique_ptr<session_impl> impl) : impl_(std::move(impl)) {} void do_read() { auto& impl = *impl_; impl.socket.async_read_some( boost::asio::buffer(impl.data, max_length), [impl = std::move(impl_)](boost::system::error_code ec, std::size_t length) mutable { if (ec) { return; } session(std::move(impl)).do_write(length); }); } void do_write(std::size_t length) { ... } auto constexpr max_length = 1024; struct session_impl { session_impl(tcp::socket socket) : socket_(std::move(socket)) {} tcp::socket socket_; char data_[max_length]; }; }; ... session(std::move(socket)).start(); вт, 21 сент. 2021 г. в 18:02, Andrzej Krzemienski via Boost <boost@lists.boost.org>:
wt., 21 wrz 2021 o 16:50 Vinnie Falco via Boost <boost@lists.boost.org> napisał(a):
On Tue, Sep 21, 2021 at 7:34 AM Andrzej Krzemienski via Boost <boost@lists.boost.org> wrote:
I am not trying to solve any specific problem. It just strikes me that a shared_ptr is used in a demo example for the library. I was always of the opinion that a shared_ptr is often abused as a way of doing an ad-hoc GC.
In theory it should work since the echo protocol is half-duplex. What happens when you switch it to unique_ptr? Move-only handlers should work, but it is possible that Chris missed a place that is still doing a copy.
It breaks when I pass a callback (completion handler), for instance in:
void do_read() { auto self(shared_from_this()); socket_.async_read_some(boost::asio::buffer(data_, max_length), [this, *self*](boost::system::error_code ec, std::size_t length) { if (!ec) { do_write(length); } }); }
I would need to move the data inside the lambda capture, but if I do it, the subsequent call to socket_.async_read_some() is UB.
In order for this to work, the function `async_read_some()` would have to pass the socket back to my handler after it has performed the read.
Regards, &rzej;
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