Swift — Methods

Instance methods

class Counter {
    var count = 0

    func increment() {
        count += 1
    }

    func increment(by amount: Int) {
        count += amount
    }

    func reset() {
        count = 0
    }
}

let c = Counter()
c.increment()
c.increment(by: 5)
print(c.count) // 6

Mutating methods

struct Point {
    var x: Double
    var y: Double

    mutating func moveBy(dx: Double, dy: Double) {
        x += dx
        y += dy
    }
}

var p = Point(x: 0, y: 0)
p.moveBy(dx: 3, dy: 4)
print(p) // Point(x: 3.0, y: 4.0)

Type methods

class MathHelper {
    static func square(_ x: Int) -> Int {
        x * x
    }

    static let pi = 3.14159
}

print(MathHelper.square(5)) // 25
print(MathHelper.pi)

Self

struct Point {
    var x: Double
    var y: Double

    func isOrigin() -> Bool {
        self.x == 0 && self.y == 0
    }
}

let p = Point(x: 0, y: 0)
print(p.isOrigin()) // true

Mini Practice

Write Swift code that:

1. Creates a class with instance methods
2. Uses a mutating method on a struct
3. Creates a type method with static
4. Demonstrates self keyword

Up Next

In the next lesson, you'll learn about Protocols — defining contracts in Swift.