Swift — Structs

Basic struct

struct Point {
    var x: Double
    var y: Double

    func distance(to other: Point) -> Double {
        let dx = x - other.x
        let dy = y - other.y
        return sqrt(dx * dx + dy * dy)
    }
}

let p1 = Point(x: 0, y: 0)
let p2 = Point(x: 3, y: 4)
print(p1.distance(to: p2)) // 5.0

Properties

struct Temperature {
    var celsius: Double {
        didSet {
            print("Temperature set to \(celsius)°C")
        }
    }

    var fahrenheit: Double {
        get { celsius * 9 / 5 + 32 }
        set { celsius = (newValue - 32) * 5 / 9 }
    }
}

var t = Temperature(celsius: 100)
print(t.fahrenheit) // 212.0
t.fahrenheit = 32
print(t.celsius)    // 0.0

Methods

struct Counter {
    var count = 0

    mutating func increment() {
        count += 1
    }

    mutating func reset() {
        count = 0
    }
}

var c = Counter()
c.increment()
c.increment()
print(c.count) // 2

Initializers

struct Size {
    var width: Double
    var height: Double

    init(width: Double = 0, height: Double = 0) {
        self.width = width
        self.height = height
    }
}

let s1 = Size(width: 10, height: 5)
let s2 = Size() // 0, 0

Value semantics

struct Point {
    var x: Double
    var y: Double
}

let p1 = Point(x: 1, y: 2)
var p2 = p1
p2.x = 10

print(p1.x) // 1 (unchanged)
print(p2.x) // 10

Protocol conformance

struct Point: CustomStringConvertible {
    var x: Double
    var y: Double

    var description: String {
        "(\(x), \(y))"
    }
}

let p = Point(x: 3, y: 4)
print(p) // (3.0, 4.0)

Mini Practice

Write Swift code that:

1. Creates a struct with computed properties
2. Uses mutating methods
3. Demonstrates value semantics
4. Conforms to a protocol

Up Next

In the next lesson, you'll learn about Classes — reference types in Swift.