why.cpp

#include <iostream>
#include <asio.hpp>
#include <array>

using asio::ip::tcp;
using asio::buffer;

void handle_with_future(tcp::socket& client)
{
    std::future<std::size_t> bytes_written = client.async_write_some(buffer("Welcome to my nightmare\n"), asio::use_future);
    std::cout << bytes_written.get() << " bytes written" << std::endl;
}

void handle_with_callback(tcp::socket& client)
{
    client.async_write_some(buffer("Welcome to callback hell\n"),[](std::error_code ec, std::size_t n){
        std::cout << n << " bytes written" << std::endl;
    });
}

void listen(tcp::acceptor& acceptor)
{
    acceptor.async_accept([&acceptor](std::error_code ec, tcp::socket client){
        if (!ec) handle_with_future(client);
        listen(acceptor);
    });
}

int main() {
    asio::io_context ctx;

    tcp::acceptor acceptor(ctx, tcp::endpoint(tcp::v4(), 1989));

    listen(acceptor);

    std::cout << std::this_thread::get_id() << std::endl;

    ctx.run();

    return EXIT_SUCCESS;
}