Gross Store

let mut foo: Felt252Dict<u32> = Default::default();

let mut foo: Felt252Dict<u32> = Default::default();
// Add a value to the dictionariy
foo.insert('bar', 42);
// Here we update the element of 'bar'
foo.insert('bar', 73);
// To retrieve a dictionary value, you can use
baz = foo.get('bar');

Instructions

A friend of yours has an old wholesale store called Gross Store.

The name comes from the quantity of the item that the store sell: it's all in gross unit.

Your friend asked you to implement a point of sale (POS) system for his store.

First, you want to build a prototype for it.

In your prototype, your system will only record the quantity.

Your friend gave you a list of measurements to help you:

1. Store the unit of measurement in your program

In order to use the measurement, you need to store the measurement in your program.

let units = units();
// Felt252Dictionary with entries like { 'dozen': 12 }

2. Create a new customer bill

You need to implement a function that create a new (empty) bill for the customer.

let bill = new_bill();
// Empty Felt252Dictionary

3. Add an item to the customer bill

To implement this, you'll need to:

• Return false if the given unit is not in the units map.
• Otherwise add the item to the customer bill, indexed by the item name, then return true.
• If the item is already present in the bill, increase its quantity by the amount that belongs to the provided unit.

let bill = new_bill();
let units = units();
let ok = add_item(bill, units, 'carrot', 'dozen');
println!(ok);
// Output: true (since dozen is a valid unit)

Note that the returned value is type bool.

4. Remove an item from the customer bill

To implement this, you'll need to:

• Return false if the given item is not in the bill. An item is considered to not be in the bill if its quantity is 0.
• Return false if the given unit is not in the units map.
• Return false if the new quantity would be less than 0.
• If the new quantity is 0, the item is considered removed from the bill, so you can return true.
• Otherwise, reduce the quantity of the item and return true.

let bill = new_bill();
let units = units();
let ok = remove_item(bill, units, 'carrot', 'dozen');
println!(ok);
// Output: false (because there are no carrots in the bill)

Note that the returned value is type bool.

5. Return the quantity of a specific item that is in the customer bill

let mut bill: Felt252Dict<u32> = Default::default();
bill.insert('carrot', 12);
bill.insert('grapes', 3);
let qty = get_item(bill, 'carrot');
println!(qty);
// Output: 12

Note that the returned value is type u32.