Showcasing a featured items gallery

Enough with the toy examples, though. Remember our Dominican Fair application from Chapter 3, Functional and Nonfunctional Requirements? Let's write a component that will select and display a few featured items from the stores that a customer saved as their favorites. This can be pretty handy when we're writing a mobile app, for example.

Let's start with a mostly C++17 implementation, which we'll update to C++20 throughout this chapter. This will include adding support for ranges.

First, let's start with some code for obtaining information about the current user:

using CustomerId = int;

CustomerId get_current_customer_id() { return 42; }

Now, let's add the store owners:

struct Merchant {
  int id;
};

The stores also need to have items in them:

struct Item {
  std::string name;
  std::optional<std::string> photo_url;
  std::string description;
  std::optional<float> price;
  time_point<system_clock> date_added...