Structs vs classes in iOS Swift - Practice Questions

Challenge - 5 Problems

🧠 Conceptual

intermediate

Difference in memory behavior between struct and class

Consider this Swift code where a struct and a class are assigned to new variables. What will be the output after modifying the new variables?

iOS Swift

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

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

var p1 = Point(x: 1, y: 1)
var p2 = p1
p2.x = 5

var l1 = Location(x: 1, y: 1)
var l2 = l1
l2.x = 5

print(p1.x, l1.x)

A 5 5

B 1 1

C 1 5

D 5 1

💡 Hint

Think about how structs and classes are copied or referenced in Swift.

Structs are value types, so p2 is a copy of p1. Changing p2.x does not affect p1.x.

Classes are reference types, so l2 and l1 refer to the same object. Changing l2.x changes l1.x.

❓ ui_behavior

intermediate

Effect of mutating method in struct vs class

Given these Swift definitions, what will be printed after calling change() on each instance?

iOS Swift

struct CounterStruct {
  var count = 0
  mutating func change() {
    count += 1
  }
}

class CounterClass {
  var count = 0
  func change() {
    count += 1
  }
}

var cs = CounterStruct()
var cc = CounterClass()
cs.change()
cc.change()
print(cs.count, cc.count)

A 0 1

B 1 1

C 1 0

D 0 0

💡 Hint

Remember that structs need mutating keyword to change properties inside methods.

Struct's change() method is marked mutating, so it can modify count.

Class methods can modify properties without mutating keyword.

Both increase count by 1.

❓ lifecycle

advanced

Deinitialization behavior difference

Which statement about deinitializers in Swift structs and classes is true?

A Neither structs nor classes have deinitializers.

B Both structs and classes can have deinitializers.

C Structs have deinitializers but classes do not.

D Only classes can have deinitializers; structs cannot.

💡 Hint

Think about which types manage memory with reference counting.

Only classes support deinitializers because they are reference types and need cleanup when instances are destroyed.

Structs are value types and do not have deinitializers.

❓ navigation

advanced

Passing struct vs class between view controllers

You pass a struct instance and a class instance from one view controller to another. What happens if you modify the struct in the second view controller?

A The original struct in the first view controller remains unchanged.

B The original struct in the first view controller is changed.

C Both struct and class instances are changed in the first view controller.

D Neither struct nor class instances can be modified in the second view controller.

💡 Hint

Consider how value and reference types behave when passed between screens.

Structs are copied when passed, so modifying the copy does not affect the original.

Classes are passed by reference, so changes affect the original.

📝 Syntax

expert

Which code snippet correctly defines a struct with a computed property?

Select the Swift code that correctly defines a struct with a computed property named 'area' that returns width * height.

A

struct Rectangle {
  var width: Int
  var height: Int
  var area: Int {
    return width * height
  }
}

B

struct Rectangle {
  var width: Int
  var height: Int
  var area {
    return width * height
  }
}

C

struct Rectangle {
  var width: Int
  var height: Int
  var area: Int() {
    return width * height
  }
}

D

struct Rectangle {
  var width: Int
  var height: Int
  func area() -> Int {
    width * height
  }
}

💡 Hint

Computed properties use var with a type and a getter block.

Option A correctly defines a computed property with type Int and a getter returning width * height.

Option A defines a method, not a computed property.

Option A has invalid syntax with Int() after property name.

Option A misses the type declaration for area.