Swift — Functions

Basic functions

func greet(name: String) -> String {
    return "Hello, \(name)!"
}

print(greet(name: "Alice"))

Multiple return values

func minMax(_ array: [Int]) -> (min: Int, max: Int)? {
    guard let first = array.first else { return nil }
    var min = first, max = first
    for value in array {
        if value < min { min = value }
        if value > max { max = value }
    }
    return (min, max)
}

if let result = minMax([3, 1, 4, 1, 5, 9]) {
    print("Min: \(result.min), Max: \(result.max)")
}

Default parameters

func greet(name: String, greeting: String = "Hello") {
    print("\(greeting), \(name)!")
}

greet(name: "Alice")           // Hello, Alice!
greet(name: "Bob", greeting: "Hi") // Hi, Bob!

Variadic parameters

func sum(_ numbers: Int...) -> Int {
    numbers.reduce(0, +)
}

print(sum(1, 2, 3))       // 6
print(sum(1, 2, 3, 4, 5)) // 15

inout parameters

func swap(_ a: inout Int, _ b: inout Int) {
    let temp = a
    a = b
    b = temp
}

var x = 1, y = 2
swap(&x, &y)
print(x, y) // 2 1

Closures

// Basic closure
let add = { (a: Int, b: Int) -> Int in
    return a + b
}
print(add(3, 4)) // 7

// Trailing closure
let nums = [1, 2, 3, 4, 5]
let evens = nums.filter { $0 % 2 == 0 }
print(evens) // [2, 4]

// Shorthand
let doubled = nums.map { $0 * 2 }
print(doubled) // [2, 4, 6, 8, 10]

Higher-order functions

func applyTwice(_ f: (Int) -> Int, _ x: Int) -> Int {
    f(f(x))
}

let double = { $0 * 2 }
print(applyTwice(double, 3)) // 12

Mini Practice

Write Swift code that:

1. Creates a function with default parameters
2. Returns multiple values from a function
3. Uses a closure with trailing closure syntax
4. Chains filter, map, and reduce

Up Next

In the next lesson, you'll learn about Closures — functional programming in Swift.