Gross Store

map[KeyType]ElementType

  // With map literal
  foo := map[string]int{}

  // or with make function
  foo := make(map[string]int)

  // Add a value in a map with the `=` operator:
  foo["bar"] = 42
  // Here we update the element of `bar`
  foo["bar"] = 73
  // To retrieve a map value, you can use
  baz := foo["bar"]
  // To delete an item from a map, you can use
  delete(foo, "bar")

  value, exists := foo["baz"]
  // If the key "baz" does not exist,
  // value: 0; exists: false

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.

units := Units()
fmt.Println(units)
// Output: map[...] 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.

bill := NewBill()
fmt.Println(bill)
// Output: map[]

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.

bill := NewBill()
units := Units()
ok := AddItem(bill, units, "carrot", "dozen")
fmt.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
• 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, completely remove the item from the bill then return true.
• Otherwise, reduce the quantity of the item and return true.

bill := NewBill()
units := Units()
ok := RemoveItem(bill, units, "carrot", "dozen")
fmt.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

To implement this, you'll need to:

• Return 0 and false if the item is not in the bill.
• Otherwise, return the quantity of the item in the bill and true.

bill := map[string]int{"carrot": 12, "grapes": 3}
qty, ok := GetItem(bill, "carrot")
fmt.Println(qty)
// Output: 12
fmt.Println(ok)
// Output: true

Note that the returned value are types int and bool.