Welcome to Gross Store on Exercism's Go Track. If you need help running the tests or submitting your code, check out HELP.md. If you get stuck on the exercise, check out HINTS.md, but try and solve it without using those first :)

Introduction

In go, map is a built-in data type that maps keys to values. In other programming language, you might be familiar with the concept of map as a dictionary, hash table, key/value store or an associative array.

Syntactically, map looks like this:

map[KeyType]ElementType

It is also important to know that each key is unique, meaning that assigning the same key twice will overwrite the value of the corresponding key.

To create a map, you can do:

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

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

Here are some operations that you can do with a map

  // 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")

If you try to retrieve the value for a key which does not exist in the map, it will return the zero value of the value type. This can confuse you, especially if the default value of your ElementType (for example, 0 for an int), is a valid value. To check whether a key exists in your map, you can use

  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:

Unit	Score
quarter_of_a_dozen	3
half_of_a_dozen	6
dozen	12
small_gross	120
gross	144
great_gross	1728

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.

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.

Source

Created by

@chocopowwwa

Contributed to by

@MiroslavGatsanoga