Why classes exist alongside structs in Swift - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a struct in Swift.

Swift

struct Person { [1] 
    var name: String
}

Drag options to blanks, or click blank then click option'

A(

B<

C[

D{

Attempts:

3 left

💡 Hint

Common Mistakes

Using parentheses or square brackets instead of curly braces.

The struct body must be enclosed in curly braces { }.

2fill in blank

medium

Complete the code to create an instance of a class in Swift.

Swift

let person = [1]()

Drag options to blanks, or click blank then click option'

APerson

Bstruct Person

Cclass Person

Dfunc Person

Attempts:

3 left

💡 Hint

Common Mistakes

Including 'class' or 'struct' keywords when creating an instance.

To create an instance, use the class name followed by parentheses.

3fill in blank

hard

Fix the error in the code to correctly copy a struct instance.

Swift

var person1 = Person(name: "Alice")
var person2 = [1]

Drag options to blanks, or click blank then click option'

Aperson1()

B&person1

Cperson1

DPerson

Attempts:

3 left

💡 Hint

Common Mistakes

Using & to reference the variable, which is not needed for structs.

Assigning one struct instance to another copies the value.

4fill in blank

hard

Fill both blanks to show how classes behave differently from structs when assigned.

Swift

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

var personA = PersonClass(name: "Bob")
var personB = [1]
personB.name = "Charlie"
print(personA.name) // [2]

Drag options to blanks, or click blank then click option'

ApersonA

B"Bob"

C"Charlie"

DPersonClass(name: "Bob")

Attempts:

3 left

💡 Hint

Common Mistakes

Thinking classes copy values like structs do.

Assigning a class instance copies the reference, so changing personB changes personA.

5fill in blank

hard

Fill all three blanks to complete the code that demonstrates why classes exist alongside structs.

Swift

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

class Circle {
    var center: [1]
    var radius: Int
    init(center: [2], radius: Int) {
        self.center = center
        self.radius = radius
    }
}

let centerPoint = Point(x: 0, y: 0)
let circle1 = Circle(center: centerPoint, radius: 5)
let circle2 = circle1
circle2.center.x = 10
print(circle1.center.x) // [3]

Drag options to blanks, or click blank then click option'

APoint

BCircle

C0

D10

Attempts:

3 left

💡 Hint

Common Mistakes

Assuming changing circle2.center.x changes circle1.center.x because Circle is a class.

The class Circle holds a struct Point. Changing circle2.center.x does not affect circle1.center.x because Point is a value type.

Practice

1. Why do classes exist alongside structs in Swift?

easy

A. Because classes cannot store data, only methods

B. Because structs are slower than classes in all cases

C. Because classes support shared references and inheritance, while structs do not

D. Because structs allow inheritance but classes do not

Solution

1. Step 1: Understand the difference between classes and structs

   Structs are value types, meaning each copy is independent. Classes are reference types, meaning multiple variables can share the same instance.

2. Step 2: Identify why classes are needed

   Classes allow shared data through references and support inheritance, which structs do not.

3. Final Answer:

   Because classes support shared references and inheritance, while structs do not -> Option C

4. Quick Check:

   Classes = shared references + inheritance [OK]

Hint: Classes share data and support inheritance; structs do not [OK]

Common Mistakes:

• Thinking structs support inheritance
• Believing classes cannot store data
• Assuming structs are always slower

2. Which of the following is the correct way to declare a class in Swift?

easy

A. struct MyClass { var name: String }

B. class MyClass { var name: String }

C. func MyClass() { var name: String }

D. let MyClass = class { var name: String }

Solution

1. Step 1: Recall Swift syntax for class declaration

   Classes in Swift are declared using the keyword class followed by the class name and braces.

2. Step 2: Check each option

   class MyClass { var name: String } correctly uses class MyClass { var name: String }. struct MyClass { var name: String } uses struct, not class. func MyClass() { var name: String } uses func, which is incorrect. let MyClass = class { var name: String } uses invalid syntax.

3. Final Answer:

   class MyClass { var name: String } -> Option B

4. Quick Check:

   Class declaration uses 'class' keyword [OK]

Hint: Use 'class' keyword to declare a class in Swift [OK]

Common Mistakes:

• Using 'struct' instead of 'class'
• Trying to declare class inside a function
• Incorrect syntax with 'let' or 'func'

3. What will be the output of this Swift code?

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

var p1 = Person(name: "Alice")
var p2 = p1
p2.name = "Bob"
print(p1.name)

medium

A. Bob

B. Alice

C. Compilation error

D. nil

Solution

1. Step 1: Understand class reference behavior

   Classes are reference types, so p1 and p2 point to the same object.

2. Step 2: Analyze the code changes

   Changing p2.name to "Bob" changes the shared object. Printing p1.name shows "Bob".

3. Final Answer:

   Bob -> Option A

4. Quick Check:

   Class variables share references, so name = Bob [OK]

Hint: Classes share instances; changing one changes all references [OK]

Common Mistakes:

• Thinking p1 and p2 are independent copies
• Expecting 'Alice' as output
• Confusing class with struct behavior

4. Identify the error in this Swift code that tries to use inheritance with a struct:

struct Vehicle {
  var speed: Int
}

struct Car: Vehicle {
  var brand: String
}

medium

A. Cannot declare variables inside structs

B. Missing initializer in Car struct

C. Syntax error: colon should be replaced with comma

D. Structs cannot inherit from other structs or classes

Solution

1. Step 1: Understand inheritance rules in Swift

   In Swift, only classes support inheritance. Structs cannot inherit from other structs or classes.

2. Step 2: Analyze the code

   The code tries to make Car inherit from Vehicle, both structs, which is invalid.

3. Final Answer:

   Structs cannot inherit from other structs or classes -> Option D

4. Quick Check:

   Inheritance = classes only, structs no [OK]

Hint: Only classes support inheritance, not structs [OK]

Common Mistakes:

• Thinking structs can inherit
• Confusing initializer errors with inheritance
• Misreading colon syntax as error

5. You want to create a data model where multiple parts of your app share and modify the same user profile data. Which Swift type should you choose and why?

hard

A. Use a class because it allows shared references and identity

B. Use a class because structs cannot store properties

C. Use a struct because it supports inheritance for flexibility

D. Use a struct because it copies data safely between parts

Solution

1. Step 1: Identify the need for shared data

   The requirement is that multiple parts share and modify the same user profile data, meaning shared references are needed.

2. Step 2: Choose the correct Swift type

   Classes are reference types that allow shared references and identity, so changes in one place reflect everywhere. Structs copy data, so changes do not propagate.

3. Final Answer:

   Use a class because it allows shared references and identity -> Option A

4. Quick Check:

   Shared data needs class reference type [OK]

Hint: Shared mutable data needs classes, not structs [OK]

Common Mistakes:

• Choosing structs for shared mutable data
• Thinking structs support inheritance
• Believing classes cannot store properties