Comparing structs vs classes decision in Swift - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a struct named Person.

Swift

struct [1] {
    var name: String
    var age: Int
}

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

APerson

Bclass

Cvar

Dfunc

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'class' instead of the struct name.

Forgetting to name the struct.

The keyword Person is the name of the struct we want to define.

2fill in blank

medium

Complete the code to create an instance of the struct Person.

Swift

let person = [1](name: "Alice", age: 30)

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

Afunc

Bclass

Cstruct

DPerson

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'class' or 'struct' keywords instead of the struct name.

Trying to call a function that does not exist.

To create an instance of a struct, use its name as a function.

3fill in blank

hard

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

Swift

var person1 = Person(name: "Bob", age: 25)
var person2 = person1
person2.name = [1]

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

ACharlie

Bperson1

C"Charlie"

Dname

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting to put quotes around the string.

Assigning a variable name instead of a string.

To assign a new name, use a string literal with quotes.

4fill in blank

hard

Fill both blanks to define a class and create its instance.

Swift

[1] PersonClass {
    var name: String
    init(name: String) {
        self.name = name
    }
}
let person = [2](name: "Dana")

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

Aclass

Bstruct

CPersonClass

DPersonStruct

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'struct' instead of 'class' to define a class.

Using the wrong name when creating an instance.

Use class to define a class and the class name to create an instance.

5fill in blank

hard

Fill all three blanks to compare struct and class behavior.

Swift

var struct1 = Person(name: "Eve", age: 40)
var struct2 = struct1
struct2.age [1] 41

var class1 = [2](name: "Frank")
var class2 = class1
class2.name [3] "George"

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

A=

BPersonClass

C!=

DPersonStruct

Attempts:

3 left

💡 Hint

Common Mistakes

Using '!=' instead of '=' for assignment.

Confusing struct and class names.

Use = to assign new values. PersonClass is the class used. Structs copy values, classes share references.

Practice

1. Which statement best describes when to use a struct instead of a class in Swift?

easy

A. Use struct when you want to share data between multiple parts of your app.

B. Use struct when you need inheritance and shared references.

C. Use struct for simple data that should be copied when assigned or passed.

D. Use struct only for UI elements like views.

Solution

1. Step 1: Understand struct behavior

   Structs are value types, meaning they are copied when assigned or passed around.

2. Step 2: Compare with class behavior

   Classes are reference types, shared by multiple references and support inheritance.

3. Final Answer:

   Use struct for simple data that should be copied when assigned or passed. -> Option C

4. Quick Check:

   Structs = copied data [OK]

Hint: Structs copy data; classes share references [OK]

Common Mistakes:

• Confusing structs with classes as reference types
• Thinking structs support inheritance
• Using structs for shared mutable state

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

easy

A. class Person { var name: String }

B. struct Person { var name: String }

C. struct Person: Class { var name: String }

D. class Person: struct { var name: String }

Solution

1. Step 1: Recall struct declaration syntax

   In Swift, structs are declared with the keyword struct followed by the name and braces.

2. Step 2: Check each option

   struct Person { var name: String } is correct. Using class is incorrect for structs. Structs cannot inherit from Class, and classes cannot inherit from struct.

3. Final Answer:

   struct Person { var name: String } -> Option B

4. Quick Check:

   Struct declaration = struct Name { } [OK]

Hint: Structs start with 'struct' keyword, not 'class' [OK]

Common Mistakes:

• Using 'class' keyword to declare a struct
• Trying to inherit from a class in a struct
• Mixing struct and class syntax

3. Consider this Swift code:

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

var p1 = Point(x: 1, y: 2)
var p2 = p1
p2.x = 10
print(p1.x)

What is the output?

medium

A. 1

B. 10

C. 0

D. Compilation error

Solution

1. Step 1: Understand struct copying behavior

   Assigning p1 to p2 copies the data because Point is a struct (value type).

2. Step 2: Analyze mutation effect

   Changing p2.x to 10 does not affect p1.x, which remains 1.

3. Final Answer:

   1 -> Option A

4. Quick Check:

   Struct copy means original unchanged = 1 [OK]

Hint: Structs copy on assignment; original stays same [OK]

Common Mistakes:

• Assuming p1.x changes when p2.x changes
• Confusing structs with classes (reference types)
• Expecting runtime error on mutation

4. This Swift code tries to share data between two variables:

class Counter {
  var count = 0
}

var c1 = Counter()
var c2 = c1
c2.count = 5
print(c1.count)

But the output is not as expected. What is the problem?

medium

A. Counter is a class, so c1 and c2 share the same instance

B. Counter is a class, but c2 is a copy, so changes don't reflect

C. Counter should be a struct to share data

D. Counter needs to conform to a protocol to share data

Solution

1. Step 1: Identify class reference behavior

   Classes are reference types, so c1 and c2 point to the same object.

2. Step 2: Understand shared mutation

   Changing c2.count to 5 changes the shared instance, so c1.count also becomes 5.

3. Final Answer:

   Counter is a class, so c1 and c2 share the same instance -> Option A

4. Quick Check:

   Classes share references = shared data [OK]

Hint: Classes share instances; structs copy data [OK]

Common Mistakes:

• Thinking classes copy on assignment
• Expecting structs to share data
• Believing protocols affect sharing automatically

5. You are designing a Swift app that tracks user sessions. Each session has a unique ID and mutable state shared across multiple parts of the app. Which type should you choose and why?

Options:
A) Use a struct because it copies data and avoids bugs.
B) Use a class because it allows shared mutable state with identity.
C) Use a struct with inheritance to share state.
D) Use a class but avoid mutability to keep data safe.

hard

A. Use a struct because it copies data and avoids bugs.

B. Use a class but avoid mutability to keep data safe.

C. Use a struct with inheritance to share state.

D. Use a class because it allows shared mutable state with identity.

Solution

1. Step 1: Analyze requirements for shared mutable state

   The session data must be shared and mutable across multiple parts, requiring a single shared instance.

2. Step 2: Choose between struct and class

   Structs copy data, so changes in one copy won't reflect elsewhere. Classes share references and support identity, fitting the need.

3. Step 3: Evaluate other options

   Structs do not support inheritance, so Use a struct with inheritance to share state. is invalid. Avoiding mutability in classes (Use a class but avoid mutability to keep data safe.) contradicts the requirement for mutable shared state.

4. Final Answer:

   Use a class because it allows shared mutable state with identity. -> Option D

5. Quick Check:

   Shared mutable state = class [OK]

Hint: Shared mutable data needs class, not struct [OK]

Common Mistakes:

• Choosing struct for shared mutable state
• Thinking structs support inheritance
• Avoiding mutability in classes when needed