Comment by gpderetta

In C++ (with a bit of help from boost).

   bool transfer(boost::synchronized<Account>& sync_from,
                 boost::synchronized<Account>& sync_to, int amount) {
         auto [from, to] =  synchronize(sync_from, sync_to);
         if (from->withdraw(amount)) {
            to->deposit(amount)
            return true;
         } else {
            return false
         }           
   }

Hopefully synchronized will make it into the standard library at some point, in the meantime it is not terribly hard to write it yourself if you do not want a boost dependency.