Why classes exist alongside structs in Swift - Challenge Your Understanding

Challenge - 5 Problems

🧠 Conceptual

intermediate

Why use classes instead of structs in Swift?

In Swift, both classes and structs can store data and have methods. But classes have a feature that structs do not. What is the main reason to choose a class over a struct?

A Structs can only store numbers, while classes can store any type of data.

B Classes support inheritance, allowing one class to inherit properties and methods from another.

C Structs cannot have methods, but classes can.

D Classes are always faster than structs because they use less memory.

💡 Hint

Think about how you can create a new type based on an existing one.

Classes support inheritance, which means you can create a new class based on an existing class, reusing and extending its behavior. Structs do not support inheritance.

❓ Predict Output

intermediate

What is the output of this Swift code using class and struct?

Consider this Swift code:

struct PointStruct {
    var x: Int
    var y: Int
}

class PointClass {
    var x: Int
    var y: Int
    init(x: Int, y: Int) {
        self.x = x
        self.y = y
    }
}

var a = PointStruct(x: 1, y: 1)
var b = a
b.x = 2

var c = PointClass(x: 1, y: 1)
var d = c
d.x = 2

print(a.x)
print(c.x)

What will be printed?

A

2
1

B

2
2

C

1
1

D

1
2

💡 Hint

Think about how structs and classes are copied or referenced.

Structs are value types, so when you assign 'a' to 'b', 'b' gets a copy. Changing 'b.x' does not affect 'a.x'. Classes are reference types, so 'c' and 'd' refer to the same object. Changing 'd.x' changes 'c.x'.

🔧 Debug

advanced

Why does this Swift code cause a compile error?

Look at this Swift code:

struct Person {
    var name: String
    mutating func changeName(newName: String) {
        name = newName
    }
}

Why does this code cause a compile error?

A Because 'changeName' tries to modify a property in a struct method that is not marked as 'mutating'.

B Because structs cannot have functions that modify properties.

C Because 'name' is a constant and cannot be changed.

D Because 'newName' parameter is not optional.

💡 Hint

Think about how structs handle methods that change their own data.

In Swift, methods that modify properties of a struct must be marked with the 'mutating' keyword. Without it, the compiler prevents modification inside the method.

📝 Syntax

advanced

Which Swift code correctly defines a class with a deinitializer?

Choose the correct Swift code that defines a class with a deinitializer that prints "Goodbye" when the object is destroyed.

A

class MyClass {
    destructor {
        print("Goodbye")
    }
}

B

class MyClass {
    func deinit() {
        print("Goodbye")
    }
}

C

class MyClass {
    deinit {
        print("Goodbye")
    }
}

D

class MyClass {
    deinitializer() {
        print("Goodbye")
    }
}

💡 Hint

Look for the special keyword Swift uses for cleanup code in classes.

Swift uses 'deinit' without parentheses to define a deinitializer. It runs when the class instance is about to be destroyed.

🚀 Application

expert

How many instances are created and shared in this Swift code?

Consider this Swift code:

class Counter {
    var count = 0
}

var c1 = Counter()
var c2 = c1
c2.count += 1

struct Wrapper {
    var counter: Counter
}

var w1 = Wrapper(counter: Counter())
var w2 = w1
w2.counter.count += 1

print(c1.count)
print(w1.counter.count)

What will be printed?

A

1
1

B

1
0

C

0
1

D

0
0

💡 Hint

Remember how classes and structs behave when assigned and copied.

c1 and c2 refer to the same Counter instance, so incrementing c2.count changes c1.count to 1.
w1 and w2 are structs (value types), so w2 is a copy of w1. However, the 'counter' property is a reference to a class instance (reference type), so w1.counter and w2.counter refer to the same Counter object. Incrementing w2.counter.count changes w1.counter.count to 1.