Keeping track of orders with actors

When it comes to keeping track of our orders, we could simply add a HashMap to our order book and add a couple of other messages that can be sent to the order book actor. This is one approach. We are getting into territory where there are no clear correct approaches, and people within the community debate on the best approaches to solve problems. In this chapter, we will get used to creating actors and managing multiple actors in Tokio by creating two new actors. One actor will merely keep track of our stock purchases, while the other actor will send messages to the order tracker to get the state of our orders.

First, we need to create a separate file in src/order_tracker.rs. In this file, we initially need to import what we need to handle the collection of stocks and the channels that enable the connections between the actors:

use tokio::sync::{mpsc, oneshot};
use std::collections::HashMap;

Then, we need to create the message struct for...