Cheatsheet

// ===== Variables + types =====
let pi = 3.14
var count = 0
let name: String = "Alex"
let maybe: String? = nil
let forced = maybe!     // crash if nil — use sparingly

// Collections:
let nums = [1, 2, 3]
let ages: [String: Int] = ["Alex": 30]
let tags: Set<String> = ["vip", "beta"]

// ===== Control flow =====
if let value = maybe { print(value) }
guard let value = maybe else { return }

for n in 1...10 { print(n) }
while count < 5 { count += 1 }

switch n {
case 0: print("zero")
case 1...9: print("small")
default: print("big")
}

// ===== Functions =====
func greet(_ name: String, with greeting: String = "Hello") -> String {
  "\(greeting), \(name)"
}
greet("Alex")
greet("Sam", with: "Hi")

// ===== Structs + classes =====
struct Point { var x: Double; var y: Double }     // value type
class Counter { var n = 0 }                        // reference type

// ===== Records via struct + Codable =====
struct User: Codable {
  let id: UUID
  let email: String
  let name: String
}

// ===== Protocols =====
protocol Describable { var description: String { get } }
extension User: Describable {
  var description: String { name }
}

// ===== Generics =====
func first<T>(_ xs: [T]) -> T? { xs.first }

// ===== Enums (with associated values) =====
enum Result<T> {
  case success(T)
  case failure(Error)
}

// ===== Optionals + chaining =====
let len = user?.profile?.bio?.count ?? 0

// ===== async / await =====
func fetch(_ url: URL) async throws -> Data {
  let (data, _) = try await URLSession.shared.data(from: url)
  return data
}

// Parallel:
async let a = fetch(url1)
async let b = fetch(url2)
let (da, db) = try await (a, b)

// ===== Error handling =====
enum AppError: Error { case notFound }

do {
  let user = try await loadUser()
} catch AppError.notFound {
  print("not found")
} catch {
  print(error)
}

// ===== SwiftUI =====
struct CounterView: View {
  @State private var count = 0
  var body: some View {
    VStack {
      Text("\(count)").font(.title)
      Button("+1") { count += 1 }
    }
  }
}

// State management:
// @State        local to view
// @Binding       passed-down 2-way
// @ObservedObject  view-supplied
// @StateObject   view-owned
// @EnvironmentObject  shared across view hierarchy
// @AppStorage    UserDefaults-backed
// @SceneStorage  per-scene

// ===== Lists =====
NavigationStack {
  List(users) { user in
    NavigationLink(user.name, destination: ProfileView(user: user))
  }
  .navigationTitle("Users")
}

// ===== Forms =====
Form {
  TextField("Email", text: $email)
  SecureField("Password", text: $password)
  Toggle("Remember me", isOn: $remember)
}

// ===== Modifiers =====
.padding()
.background(Color.blue)
.cornerRadius(8)
.shadow(radius: 4)
.frame(width: 200, height: 100)

// ===== Patterns =====
// - struct + value semantics by default
// - Optional types in signatures
// - async / await over completion handlers
// - SwiftUI declarative composition
// - Codable for JSON

// ===== Pitfalls =====
// - Force-unwrap (!) -> crashes
// - Capturing self in closures (use [weak self])
// - Massive view controllers (UIKit)
// - Mixing Combine + async/await without a strategy

// swift run | test | build | package init