std::optional

I have the following example code, that implements a asynchronous server using boost::asio

I am trying to understand the code. The questions I have regarding the code are as follows

In function async_accept() in class server, the first statement is

socket.emplace(io_context)

From what I understand, this line call the socket constructor, create a socket. This socket is then passed to the session, usign std::move().

When the async_accept() is called again, in the last line of the funtion, a new socket is created. Is my understanding correct? Am I missing something?

#include <iostream>
#include <optional>
#include <boost/asio.hpp>

class session : public std::enable_shared_from_this<session>
{
public:

    session(boost::asio::ip::tcp::socket&& socket)
    : socket(std::move(socket))
    {
    }

    void start()
    {
        boost::asio::async_read_until(socket, streambuf, '\n', [self = shared_from_this()] (boost::system::error_code error, std::size_t bytes_transferred)
        {
            std::cout << std::istream(&self->streambuf).rdbuf();
        });
    }

private:

    boost::asio::ip::tcp::socket socket;
    boost::asio::streambuf streambuf;
};

class server
{
public:

    server(boost::asio::io_context& io_context, std::uint16_t port)
    : io_context(io_context)
    , acceptor  (io_context, boost::asio::ip::tcp::endpoint(boost::asio::ip::tcp::v4(), port))
    {
    }

    void async_accept()
    {
        socket.emplace(io_context);

        acceptor.async_accept(*socket, [&] (boost::system::error_code error)
        {
            std::make_shared<session>(std::move(*socket))->start();
            async_accept();
        });
    }

private:

    boost::asio::io_context& io_context;
    boost::asio::ip::tcp::acceptor acceptor;
    std::optional<boost::asio::ip::tcp::socket> socket;
};

int main()
{
    boost::asio::io_context io_context;
    server srv(io_context, 15001);
    srv.async_accept();
    io_context.run();
    return 0;
}