Extension syntax in Swift - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of extension method call

What is the output of this Swift code using an extension?

Swift

extension Int {
    func squared() -> Int {
        return self * self
    }
}

let number = 4
print(number.squared())

A Compilation error

B 8

C 16

D 4

💡 Hint

Think about what multiplying a number by itself means.

The extension adds a method 'squared' to Int that returns the number multiplied by itself. 4 * 4 equals 16.

❓ Predict Output

intermediate

Extension adding computed property

What will be printed by this Swift code that uses an extension with a computed property?

Swift

extension String {
    var isLong: Bool {
        return self.count > 5
    }
}

let word = "Swift"
print(word.isLong)

A false

B true

C Compilation error

D nil

💡 Hint

Count the letters in the word "Swift".

The word "Swift" has 5 letters, which is not greater than 5, so isLong returns false.

🔧 Debug

advanced

Why does this extension cause a compile error?

This Swift extension code causes a compile error. What is the reason?

Swift

extension Int {
    func multiply(by: Int) -> Int {
        return self * by
    }

    func multiply(by: Int) -> Int {
        return self * by * 2
    }
}

A Missing return statement in one method

B Syntax error due to missing braces

C Extension cannot add methods to Int

D Cannot have two methods with the same name and parameters in one extension

💡 Hint

Think about method overloading rules in Swift.

Swift does not allow two methods with the same name and parameter types in the same scope, even in extensions.

📝 Syntax

advanced

Identify the correct extension syntax

Which option shows the correct syntax to add a method named 'greet' to the String type using an extension?

A

extension String {
    func greet() {
        print("Hello, \(self)!")
    }
}

B

extension String {
    greet() {
        print("Hello")
    }
}

C

extension String {
    func greet {
        print("Hi")
    }
}

D

extension String {
    func greet() -> String {
        print("Hello")
    }
}

💡 Hint

Remember the full function declaration syntax in Swift.

Option A correctly declares a method with 'func', parentheses, and a body. Others miss parentheses or return types or have syntax errors.

🚀 Application

expert

Using extension to add a protocol conformance

Given this protocol and struct, which extension correctly adds conformance to the protocol by implementing the required method?

Swift

protocol Describable {
    func describe() -> String
}

struct Car {
    let brand: String
    let year: Int
}

A

extension Car {
    func describe() -> String {
        return "Car brand: \(brand), year: \(year)"
    }
}

B

extension Car: Describable {
    func describe() -> String {
        return "Car brand: \(brand), year: \(year)"
    }
}

C

extension Describable {
    func describe() -> String {
        return "Describable object"
    }
}

D

extension Car: Describable {
    func describe() {
        print("Car brand: \(brand), year: \(year)")
    }
}

💡 Hint

To conform to a protocol, implement all required methods with correct signatures in an extension that declares conformance.

Option B correctly declares Car conforms to Describable and implements describe() returning String. Option B lacks conformance declaration. Option B extends the protocol, not Car. Option B has wrong method signature (missing return type).