Swift Cheat Sheet

Swift syntax, optional handling, structs versus classes, protocols, and closures for building type-safe iOS and macOS applications.

2 PagesIntermediateMar 28, 2026

Basic Syntax

Variables, control flow, and printing.

swift

import Foundationlet age = 30                  // constant (let)var count = 0                  // variable (var)let name = "Ada"let pi: Double = 3.14159if age >= 18 {    print("\(name) is an adult")}for i in 0..<5 {    print("Count: \(i)")}

Optionals

Safely handling the absence of a value.

swift

var middleName: String? = nil   // optional, may hold nilif let name = middleName {      // optional binding    print("Middle name: \(name)")} else {    print("No middle name")}let display = middleName ?? "N/A"   // nil-coalescing operatorguard let unwrapped = middleName else {    fatalError("middleName was nil")}

Protocols & Closures

Interfaces and inline functions.

swift

protocol Greetable {    func greet() -> String}struct Person: Greetable {    let name: String    func greet() -> String { "Hello, \(name)" }}let numbers = [1, 2, 3, 4, 5]let doubled = numbers.map { $0 * 2 }          // closure shorthandlet sum = numbers.reduce(0) { $0 + $1 }       // 15

Core Keywords

Common Swift language keywords.

let/var- constant and mutable variable declarations
struct- value type, copied on assignment
class- reference type, shared by reference
protocol- defines a blueprint of methods/properties (like an interface)
guard- early-exit control flow requiring a condition to hold
extension- adds functionality to an existing type
Optional (?/!)- ? declares optional, ! force-unwraps
enum- value type supporting associated values and pattern matching

Pro Tip

Prefer struct over class by default in Swift — value semantics avoid unexpected shared mutable state; reach for class only when you need reference identity or inheritance.

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