Structs

Part of the Object Oriented Programming section of Coddy's Swift journey. Lesson 7 of 57.

A struct groups data and methods like a class. Swift writes a memberwise initializer for every struct, with one parameter per property, so a struct needs no init of its own:

struct Point {
    var x: Int
    var y: Int

    func distanceFromOrigin() -> Int {
        abs(x) + abs(y)
    }
}

let p = Point(x: 3, y: -4)
print(p.x)
print(p.distanceFromOrigin())

Output:

3
7

Properties with default values can be left out of the memberwise initializer:

struct Settings {
    var volume = 5
    var muted = false
}

let quiet = Settings(volume: 1)
print(quiet.volume)
print(quiet.muted)

Output:

1
false

A struct stored in a let constant cannot change at all, not even its var properties. Store it in a var to change it:

let fixed = Point(x: 1, y: 2)
// fixed.x = 5    // error: cannot assign, fixed is a let constant

var moving = Point(x: 1, y: 2)
moving.x = 5       // fine

Many of Swift's own types are structs: Int, Double, String, Array and Dictionary. Your structs behave the same way as those types: they are plain values.

struct Money {
    var cents: Int
    func formatted() -> String {
        "\(cents / 100).\(cents % 100 < 10 ? "0" : "")\(cents % 100)"
    }
}

print(Money(cents: 1250).formatted())
print(Money(cents: 305).formatted())

Output:

12.50
3.05

Challenge

Easy

Declare a struct Item with the properties name (String), price (Int, in cents) and quantity (Int). Add a method total() that returns price times quantity, and a method line() that returns 2 x tea = 350.

The supplied code reads one item per line as name,price,quantity, creates each Item with the memberwise initializer and prints line(). It then prints sum: and the sum of all totals.

Your code goes in Item.swift. main.swift holds the supplied input/output code and cannot be edited.

Try it yourself

// Supplied input/output code: keep it as it is
var input: [String] = []
while let line = readLine() { input.append(line) }
var sum = 0
for row in input {
    let p = row.split(separator: ",").map(String.init)
    let item = Item(name: p[0], price: Int(p[1])!, quantity: Int(p[2])!)
    print(item.line())
    sum += item.total()
}
print("sum: \(sum)")