Protocols in iOS Swift - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding Protocol Requirements

Given the protocol and struct below, what will be the output when calling print(user.description)?

iOS Swift

protocol Describable {
  var description: String { get }
}

struct User: Describable {
  var name: String
  var description: String {
    return "User: \(name)"
  }
}

let user = User(name: "Alice")
print(user.description)

A Alice

B User

C User: Alice

D Compilation error: missing protocol requirement

💡 Hint

Check how the description property is implemented in the struct.

The struct User conforms to Describable by implementing the description property. It returns "User: Alice" when accessed.

❓ ui_behavior

intermediate

Protocol and UIViewController Behavior

If a UIViewController conforms to a protocol with a method setupUI() and calls it inside viewDidLoad(), what happens when the view loads?

iOS Swift

protocol UISetup {
  func setupUI()
}

class MyViewController: UIViewController, UISetup {
  override func viewDidLoad() {
    super.viewDidLoad()
    setupUI()
  }
  func setupUI() {
    view.backgroundColor = .blue
  }
}

A Compilation error: UIViewController cannot conform to protocols.

B The app crashes because setupUI() is not called.

C The view background color remains default (white).

D The view background color becomes blue when the view loads.

💡 Hint

Look at when setupUI() is called and what it does.

The setupUI() method is called inside viewDidLoad(), so the background color changes to blue when the view loads.

❓ lifecycle

advanced

Protocol Extension and Method Dispatch

What will be printed when running the code below?

iOS Swift

protocol Greetable {
  func greet()
}

extension Greetable {
  func greet() {
    print("Hello from protocol extension")
  }
}

class Person: Greetable {
  func greet() {
    print("Hello from Person class")
  }
}

let p: Greetable = Person()
p.greet()

A Hello from Person class

B Hello from protocol extension

C Compilation error: greet() ambiguous

D Runtime error: method not found

💡 Hint

Consider how Swift chooses methods when a class implements a protocol method and the protocol has a default implementation.

Swift uses dynamic dispatch for class methods. Since Person implements greet(), that method is called instead of the protocol extension's default.

📝 Syntax

advanced

Protocol with Associated Type Syntax

Which option correctly declares a protocol with an associated type and a method using it?

A protocol Container { associatedtype ItemType func append(_ item: ItemType) }

B protocol Container { typealias ItemType func append(_ item: ItemType) }

C protocol Container { associatedtype ItemType func append(item: ItemType) -> Void }

D protocol Container { associatedtype ItemType func append(item: ItemType) }

💡 Hint

Look for the correct keyword to declare an associated type and method parameter syntax.

Option A correctly uses associatedtype and a method with a parameter labeled with underscore to omit external label, matching Swift syntax.

🔧 Debug

expert

Resolving Protocol Conformance Ambiguity

Given the code below, what error will the compiler produce?

iOS Swift

protocol Drawable {
  func draw()
}

extension Drawable {
  func draw() {
    print("Drawing from extension")
  }
}

class Shape: Drawable {
}

let shape = Shape()
shape.draw()

A Error: Type 'Shape' does not conform to protocol 'Drawable' because 'draw()' is not implemented

B No error; prints "Drawing from extension"

C Error: Ambiguous use of 'draw()'

D Runtime error: method 'draw()' not found

💡 Hint

Check if protocol extension provides a default implementation and if the class must implement it explicitly.

The protocol extension provides a default implementation of draw(), so Shape conforms without implementing it explicitly.