Protocol requirements (methods and properties) in Swift - Mini Project: Build & Apply

Protocol requirements (methods and properties) in Swift

📖 Scenario: You are creating a simple app to manage different types of vehicles. Each vehicle must have a name and a way to start it. You will use a protocol to define these requirements.

🎯 Goal: Build a Swift program that defines a protocol with method and property requirements, then create a struct that conforms to this protocol and implements the required method and property.

📋 What You'll Learn

Define a protocol called Vehicle with a read-only property name of type String

Add a method requirement start() in the Vehicle protocol

Create a struct called Car that conforms to the Vehicle protocol

Implement the name property and start() method in the Car struct

Print the car's name and call the start() method to show the output

💡 Why This Matters

🌍 Real World

Protocols are used in Swift to define common behavior that different types can share, such as vehicles having names and start methods.

💼 Career

Understanding protocols is essential for Swift developers to write flexible, reusable, and maintainable code in apps and frameworks.

1

Define the Vehicle protocol

Define a protocol called Vehicle with a read-only property name of type String and a method requirement start().

Swift

# Define the Vehicle protocol with a read-only property 'name' and a method 'start()'
// Your code here

Hint

Use protocol keyword. The property name should be read-only, so use { get }. The method start() has no parameters and no return value.

2

Create the Car struct conforming to Vehicle

Create a struct called Car that conforms to the Vehicle protocol. Add a stored property name of type String.

Swift

protocol Vehicle {
    var name: String { get }
    func start()
}

// Create struct Car conforming to Vehicle with a stored property 'name'
// Your code here

Hint

Use struct Car: Vehicle to conform. The name property can be a constant let. Implement the start() method inside the struct.

3

Implement the start() method

Inside the Car struct, implement the start() method to print the message: " is starting" where is the car's name.

Swift

protocol Vehicle {
    var name: String { get }
    func start()
}

struct Car: Vehicle {
    let name: String
    // Implement start() method here
    // Your code here
}

Hint

Use print with string interpolation to include the name property in the message.

4

Create a Car instance and call start()

Create a constant myCar of type Car with the name "Tesla". Then print myCar.name and call myCar.start().

Swift

protocol Vehicle {
    var name: String { get }
    func start()
}

struct Car: Vehicle {
    let name: String
    func start() {
        print("\(name) is starting")
    }
}

// Create a Car instance named myCar with name "Tesla"
// Print myCar.name and call myCar.start()
// Your code here

Hint

Create myCar with Car(name: "Tesla"). Use print(myCar.name) and myCar.start() to show the output.

Practice

1. What does a protocol in Swift require from a type that adopts it?

easy

A. To declare new methods unrelated to the protocol

B. To inherit from a superclass

C. To override all existing methods

D. To implement all the methods and properties declared in the protocol

Solution

1. Step 1: Understand protocol purpose

   Protocols define a set of methods and properties that a type must implement.

2. Step 2: Check adoption requirements

   Any type adopting a protocol must provide implementations for all its requirements.

3. Final Answer:

   To implement all the methods and properties declared in the protocol -> Option D

4. Quick Check:

   Protocol adoption = implement all requirements [OK]

Hint: Protocols require full implementation of declared methods and properties [OK]

Common Mistakes:

• Thinking protocols require inheritance from a class
• Assuming methods can be skipped
• Confusing protocol adoption with subclassing

2. Which of the following is the correct way to declare a read-only property requirement in a Swift protocol?

easy

A. var name: String { get }

B. var name: String { get set }

C. let name: String

D. func name() -> String

Solution

1. Step 1: Recall property syntax in protocols

   Read-only properties use { get } to indicate they must be readable but not necessarily writable.

2. Step 2: Analyze options

   var name: String { get } uses { get } correctly; var name: String { get set } requires read-write; let name: String is invalid in protocols; func name() -> String is a method, not a property.

3. Final Answer:

   var name: String { get } -> Option A

4. Quick Check:

   Read-only property = { get } [OK]

Hint: Use { get } for read-only property in protocols [OK]

Common Mistakes:

• Using let instead of var in protocol
• Confusing methods with properties
• Using { get set } for read-only properties

3. Consider the following Swift code:

protocol Vehicle {
    var speed: Double { get set }
    func description() -> String
}

struct Car: Vehicle {
    var speed: Double
    func description() -> String {
        return "Car speed is \(speed) km/h"
    }
}

let myCar = Car(speed: 80)
print(myCar.description())

What is the output when this code runs?

medium

A. Error: Protocol requirements not met

B. Car speed is 80.0 km/h

C. Car speed is 80 km/h

D. Car speed is km/h

Solution

1. Step 1: Check protocol conformance

   Car struct implements the required property speed and method description(), fulfilling Vehicle protocol.

2. Step 2: Analyze print output

   The description() returns "Car speed is \(speed) km/h". Since speed is 80.0 (Double), string interpolation formats it as "80.0".

3. Final Answer:

   Car speed is 80.0 km/h -> Option B

4. Quick Check:

   Protocol methods implemented = correct output [OK]

Hint: String interpolation for Double 80.0 prints '80.0' [OK]

Common Mistakes:

• Expecting 80 instead of 80.0
• Thinking protocol conformance causes error
• Missing string interpolation syntax

4. Given this protocol and struct:

protocol Shape {
    var area: Double { get }
    func perimeter() -> Double
}

struct Square: Shape {
    var side: Double
    var area: Double {
        side * side
    }
}

What is the error in the code?

medium

A. area property should be var with get set

B. side property must be a constant (let)

C. Missing implementation of perimeter() method

D. Square cannot have computed properties

Solution

1. Step 1: Check protocol requirements

   Shape protocol requires a read-only property area and a method perimeter().

2. Step 2: Verify Square struct implementation

   Square implements area as computed property but does not implement perimeter() method.

3. Final Answer:

   Missing implementation of perimeter() method -> Option C

4. Quick Check:

   All protocol methods must be implemented [OK]

Hint: All protocol methods must be implemented, or error occurs [OK]

Common Mistakes:

• Assuming computed properties are not allowed
• Thinking get set is required for read-only
• Ignoring missing method implementations

5. You want to create a protocol Identifiable that requires a read-only id property of type String and a method identify() that prints the id. Which of the following is the correct protocol and extension to provide a default implementation of identify()?

hard

A. protocol Identifiable {
var id: String { get }
func identify()
}
extension Identifiable {
func identify() {
print("ID: \(id)")
}
}

B. protocol Identifiable {
var id: String { get set }
func identify()
}
extension Identifiable {
func identify() {
print(id)
}
}

C. protocol Identifiable {
let id: String
func identify()
}
extension Identifiable {
func identify() {
print("ID is " + id)
}
}

D. protocol Identifiable {
var id: String { get }
func identify() -> String
}
extension Identifiable {
func identify() -> String {
return id
}
}

Solution

1. Step 1: Define protocol requirements

   id must be read-only, so use { get } and identify() method with no return.

2. Step 2: Provide default implementation in extension

   Extension implements identify() printing "ID: \(id)" matching protocol signature.

3. Final Answer:

   protocol Identifiable { var id: String { get }; func identify() } extension Identifiable { func identify() { print("ID: \(id)") } } -> Option A

4. Quick Check:

   Read-only property + default method in extension [OK]

Hint: Use protocol extension for default method implementations [OK]

Common Mistakes:

• Using let in protocol property
• Changing method signature in extension
• Making id writable when only read-only needed