Methods

// STRUCT METHODS
// Methods are functions that belong to a struct

// INSTANCE METHODS
struct Counter {
    var count: Int = 0

    func displayCount() {
        print("Current count: \(count)")
    }

    func isGreaterThan(_ value: Int) -> Bool {
        return count > value
    }
}

var counter = Counter()
counter.displayCount()  // Current count: 0

// MUTATING METHODS
// Methods that modify struct properties must be marked 'mutating'
struct Player {
    var name: String
    var score: Int = 0
    var level: Int = 1

    mutating func addScore(_ points: Int) {
        score += points
        print("\(name) scored \(points) points! Total: \(score)")
    }

    mutating func levelUp() {
        level += 1
        print("\(name) leveled up to \(level)!")
    }

    func status() -> String {
        return "\(name) - Level \(level), Score: \(score)"
    }
}

var player = Player(name: "Alice")
player.addScore(100)  // Alice scored 100 points!
player.levelUp()      // Alice leveled up to 2!

// SELF KEYWORD
struct Point {
    var x: Double
    var y: Double

    mutating func moveTo(x: Double, y: Double) {
        self.x = x  // self.x is property, x is parameter
        self.y = y
    }

    func distanceTo(_ other: Point) -> Double {
        let dx = self.x - other.x
        let dy = self.y - other.y
        return (dx * dx + dy * dy).squareRoot()
    }
}

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

// TYPE METHODS (Static)
struct MathHelper {
    static func square(_ n: Int) -> Int {
        return n * n
    }

    static func cube(_ n: Int) -> Int {
        return n * n * n
    }
}

print(MathHelper.square(5))  // 25
print(MathHelper.cube(3))    // 27