Protocol requirements (methods and properties) in Swift - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a struct conforming to a protocol with property requirements

What is the output of this Swift code when run?

Swift

protocol Vehicle {
    var numberOfWheels: Int { get }
    func description() -> String
}

struct Bike: Vehicle {
    var numberOfWheels: Int = 2
    func description() -> String {
        return "Bike with \(numberOfWheels) wheels"
    }
}

let myBike = Bike()
print(myBike.description())

A Runtime error

B Bike with wheels

C Compilation error: missing property implementation

D Bike with 2 wheels

💡 Hint

Check how the struct implements the protocol's property and method.

The struct Bike correctly implements the required property numberOfWheels and method description(). The print statement outputs the string with the number 2.

❓ Predict Output

intermediate

Protocol method requirement with mutating keyword

What will be printed when this Swift code runs?

Swift

protocol Toggleable {
    mutating func toggle()
}

struct LightSwitch: Toggleable {
    var isOn = false
    mutating func toggle() {
        isOn = !isOn
    }
}

var light = LightSwitch()
light.toggle()
print(light.isOn)

A true

B false

C Compilation error: missing mutating keyword

D Runtime error

💡 Hint

Look at how the toggle method changes the isOn property.

The toggle method flips the isOn boolean from false to true. The print statement outputs true.

🔧 Debug

advanced

Identify the error in protocol property implementation

Why does this Swift code fail to compile?

Swift

protocol Identifiable {
    var id: String { get set }
}

struct User: Identifiable {
    let id: String
}

A Missing method implementation

B Cannot assign let property 'id' to protocol requiring get set

C Protocol requires static property 'id'

D No error, code compiles fine

💡 Hint

Check the difference between 'let' and 'var' in property requirements.

The protocol requires a property 'id' that can be read and written (get set). The struct declares 'id' as a constant (let), which cannot be set after initialization, causing a compile error.

📝 Syntax

advanced

Correct syntax for protocol property with optional get and set

Which option correctly declares a protocol property that can be read and optionally written?

A var name: String { get set }

B var name: String { get }

C var name: String { set }

D var name: String { get optional set }

💡 Hint

Protocols specify property requirements with get and set keywords.

Option A declares a property that must be readable and writable. Option A is read-only. Option A is write-only (rare). Option A is invalid syntax.

🚀 Application

expert

Implement a protocol with a class and demonstrate property observer

Given this protocol, which class implementation correctly conforms and prints a message when the property changes?

Swift

protocol TemperatureMonitor {
    var temperature: Double { get set }
}

class Sensor: TemperatureMonitor {
    var temperature: Double = 0.0 {
        didSet {
            print("Temperature changed to \(temperature)")
        }
    }
}

let sensor = Sensor()
sensor.temperature = 25.5

A Compilation error: property observer not allowed

B No output printed

C Prints 'Temperature changed to 25.5'

D Runtime error

💡 Hint

Property observers can be used in classes to react to changes.

The class Sensor conforms to the protocol and uses didSet to print a message whenever temperature changes. Setting temperature to 25.5 triggers the print.