bank_account.cpp

#define BOOST_ASIO_NO_DEPRECATED
#include <boost/config.hpp>

#include <boost/asio/post.hpp>
#include <boost/asio/thread_pool.hpp>
#include <boost/asio/use_future.hpp>

#include <iostream>

using boost::asio::post;
using boost::asio::thread_pool;
using boost::asio::use_future;

// Traditional active object pattern.
// Member functions block until operation is finished.

class bank_account {
    int balance_ = 0;
    mutable thread_pool pool_ { 1 };

public:
    void deposit(int amount)
    {
        post(pool_, use_future([=] { balance_ += amount; })).get();
    }

    void withdraw(int amount)
    {
        post(pool_, use_future([=] {
            if (balance_ >= amount)
                balance_ -= amount;
        })).get();
    }

    int balance() const
    {
        return post(pool_, use_future([=] { return balance_; })).get();
    }
};

int main()
{
    bank_account acct;
    acct.deposit(20);
    acct.withdraw(10);
    std::cout << "balance = " << acct.balance() << "\n";

    return 0;
}