Functions and Closures

Functions are fundamental building blocks in Swift. This lesson covers function declaration, parameters, return types, closures, and higher-order functions.

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Function Basics

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

let message = greet(person: "Alice")  // "Hello, Alice!"

Functions Without Return Values

func printGreeting(for name: String) {
    print("Hello, \(name)!")
}

Multiple Return Values with Tuples

func minMax(array: [Int]) -> (min: Int, max: Int)? {
    guard !array.isEmpty else { return nil }
    var currentMin = array[0]
    var currentMax = array[0]
    for value in array[1...] {
        if value < currentMin { currentMin = value }
        if value > currentMax { currentMax = value }
    }
    return (min: currentMin, max: currentMax)
}

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

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Argument Labels and Parameter Names

Swift functions have both an argument label (used when calling) and a parameter name (used inside the function):

func move(from source: String, to destination: String) {
    print("Moving from \(source) to \(destination)")
}
move(from: "London", to: "Paris")

Omitting the Argument Label

Use _ to allow callers to omit the label: