Initializers and designated init in Swift - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Swift initializer code?

Consider the following Swift class with a designated initializer and a convenience initializer. What will be printed when creating an instance with let obj = MyClass()?

Swift

class MyClass {
    var value: Int
    
    init(value: Int) {
        self.value = value
        print("Designated init with value: \(value)")
    }
    
    convenience init() {
        self.init(value: 10)
        print("Convenience init called")
    }
}

let obj = MyClass()

A No output printed

B Convenience init called\nDesignated init with value: 10

C Designated init with value: 0\nConvenience init called

D Designated init with value: 10\nConvenience init called

💡 Hint

Remember that convenience initializers must call a designated initializer first.

The convenience initializer calls the designated initializer first, which prints the first line. Then the convenience initializer prints its own message.

❓ Predict Output

intermediate

What error does this Swift initializer code produce?

What error will this Swift class produce when compiled?

Swift

class Person {
    var name: String
    
    convenience init(name: String) {
        self.name = name
    }
}

A Error: Property 'name' not initialized before use

B Error: Convenience initializer must call a designated initializer

C No error, compiles successfully

D Error: Missing required initializer

💡 Hint

Check the rules for convenience initializers in Swift.

Convenience initializers must call a designated initializer. Here, the convenience init tries to assign a property directly without calling a designated init, causing an error.

🔧 Debug

advanced

Why does this Swift struct initializer code fail to compile?

This Swift struct has a custom initializer. Why does it fail to compile?

Swift

struct Rectangle {
    var width: Double
    var height: Double
    
    init(width: Double) {
        self.width = width
    }
}

A Error: Property 'height' not initialized before use

B Error: Structs cannot have custom initializers

C No error, compiles successfully

D Error: Initializer missing 'self' keyword

💡 Hint

All stored properties must be initialized before the initializer ends.

The property 'height' is not given a value in the initializer, so the compiler raises an error.

❓ Predict Output

advanced

What is the output of this Swift class inheritance initializer code?

Given the following Swift classes, what will be printed when creating let c = Child()?

Swift

class Parent {
    init() {
        print("Parent init")
    }
}

class Child: Parent {
    override init() {
        print("Child init start")
        super.init()
        print("Child init end")
    }
}

let c = Child()

A Child init start\nParent init\nChild init end

B Parent init\nChild init start\nChild init end

C Child init start\nChild init end\nParent init

D Parent init\nChild init end\nChild init start

💡 Hint

Remember the order of initializer calls in inheritance.

The child initializer runs its code, then calls super.init(), then continues after that call.

❓ Predict Output

expert

What is the value of 'description' after this Swift initializer code runs?

Analyze the following Swift class with a designated initializer and a computed property. What is the value of obj.description after let obj = Vehicle(type: "Car", wheels: 4)?

Swift

class Vehicle {
    var type: String
    var wheels: Int
    
    var description: String {
        "\(type) with \(wheels) wheels"
    }
    
    init(type: String, wheels: Int) {
        self.type = type
        self.wheels = wheels
    }
}

let obj = Vehicle(type: "Car", wheels: 4)

A "Vehicle with 4 wheels"

B "Car with wheels"

C "Car with 4 wheels"

D "type with wheels"

💡 Hint

Check how the computed property uses stored properties.

The computed property returns a string combining the 'type' and 'wheels' values initialized in the constructor.