Why structs are preferred in Swift - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a struct named Person with a name property.

Swift

struct [1] {
    var name: String
}

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

APerson

Bclass

Cfunc

Dvar

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'class' instead of the struct name.

Using 'func' or 'var' which are not valid struct names.

The keyword Person is the name of the struct. We use struct to declare it.

2fill in blank

medium

Complete the code to create a new instance of the struct Person.

Swift

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

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

APerson

BPerson()

Cperson

Dstruct

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'Person()' with parentheses inside the code incorrectly.

Using 'struct' keyword instead of the struct name.

To create an instance, use the struct name Person followed by parentheses with parameters.

3fill in blank

hard

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

Swift

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

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

Aperson2.name

Bperson1.name

C"Alice"

DPerson.name

Attempts:

3 left

💡 Hint

Common Mistakes

Assigning from person1.name which does not change the name.

Using Person.name which is invalid syntax.

Assigning a new string value like "Alice" to person2.name changes only person2 because structs are copied.

4fill in blank

hard

Fill both blanks to create a struct with a method that returns a greeting.

Swift

struct Greeter {
    var name: String
    func [1]() -> String {
        return "Hello, \([2])!"
    }
}

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

Agreet

Bname

CsayHello

Dself

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'sayHello' as method name but not matching the blank order.

Using 'self' instead of the property name inside the string.

The method is named greet and it returns a greeting using the name property.

5fill in blank

hard

Fill all three blanks to create a struct with a computed property that returns the full name.

Swift

struct User {
    var firstName: String
    var lastName: String
    var fullName: String {
        return [1] + " " + [2]
    }
    func printName() {
        print([3])
    }
}

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

AfirstName

BlastName

CfullName

Dname

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'name' which is not defined.

Printing 'firstName' or 'lastName' instead of 'fullName'.

The computed property fullName combines firstName and lastName. The printName method prints fullName.

Practice

1. Why are structs preferred over classes in Swift for small data types?

easy

A. Because structs allow inheritance and polymorphism

B. Because structs use more memory than classes

C. Because structs copy data, avoiding unexpected changes from shared references

D. Because structs require manual memory management

Solution

1. Step 1: Understand data copying in structs

   Structs in Swift create a copy of data when assigned or passed, so changes to one copy don't affect others.

2. Step 2: Compare with classes and shared references

   Classes use references, so multiple variables can point to the same data, causing unexpected changes.

3. Final Answer:

   Because structs copy data, avoiding unexpected changes from shared references -> Option C

4. Quick Check:

   Structs copy data = safer small data types [OK]

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

Common Mistakes:

• Thinking structs support inheritance like classes
• Believing structs use more memory than classes
• Assuming structs require manual memory management

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

easy

A. struct Person { var name: String }

B. class Person { var name: String }

C. struct Person = (name: String)

D. struct Person: String { var name }

Solution

1. Step 1: Recall Swift struct syntax

   Structs are defined using the keyword struct followed by the name and curly braces containing properties.

2. Step 2: Check each option

   struct Person { var name: String } correctly uses struct Person { var name: String }. class Person { var name: String } uses class, not struct. Options C and D have invalid syntax.

3. Final Answer:

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

4. Quick Check:

   Correct struct syntax = struct Person { var name: String } [OK]

Hint: Use 'struct Name { var property: Type }' for structs [OK]

Common Mistakes:

• Using 'class' keyword instead of 'struct'
• Incorrect property declaration syntax
• Trying to assign struct like a tuple

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

struct Point { var x: Int; var y: Int }
var p1 = Point(x: 5, y: 10)
var p2 = p1
p2.x = 20
print(p1.x)

medium

A. 5

B. 20

C. 10

D. Compilation error

Solution

1. Step 1: Understand struct copying behavior

   Assigning p1 to p2 copies the data. They are independent after assignment.

2. Step 2: Analyze the change to p2.x

   Changing p2.x to 20 does not affect p1.x, which remains 5.

3. Final Answer:

   5 -> Option A

4. Quick Check:

   Struct copy means p1.x stays 5 [OK]

Hint: Struct assignment copies data; original stays unchanged [OK]

Common Mistakes:

• Thinking p1.x changes when p2.x changes
• Confusing structs with class reference behavior
• Expecting runtime error due to assignment

4. Identify the error in this Swift code using structs:

struct Rectangle {
  var width: Int
  var height: Int
}

var rect1 = Rectangle(width: 10, height: 20)
var rect2 = rect1
rect2.width = 30
print(rect1.width)

medium

A. rect2.width cannot be changed because structs are immutable

B. rect1.width prints 30 because structs share references

C. Compilation error due to missing initializer

D. No error; rect1.width prints 10 because structs copy data

Solution

1. Step 1: Check mutability of struct instances

   Since rect2 is a variable (var), its properties can be changed.

2. Step 2: Understand copying behavior

   Assigning rect1 to rect2 copies the data. Changing rect2.width does not affect rect1.width.

3. Final Answer:

   No error; rect1.width prints 10 because structs copy data -> Option D

4. Quick Check:

   Struct copy means rect1.width stays 10 [OK]

Hint: Structs copy data; changing copy doesn't affect original [OK]

Common Mistakes:

• Assuming structs are immutable by default
• Thinking structs share references like classes
• Expecting compilation error for missing initializer

5. You want to create a simple data type to store a user's profile with name and age. Why is using a struct better than a class in Swift for this case?

hard

A. Structs use reference counting, improving performance for user data

B. Structs provide automatic copying, preventing accidental shared changes in user data

C. Structs allow inheritance, making it easier to extend user profiles

D. Structs require manual memory management, giving more control over user data

Solution

1. Step 1: Consider data safety for user profiles

   User profiles are simple data that should not change unexpectedly when copied or passed around.

2. Step 2: Compare structs and classes for this use

   Structs copy data automatically, so each copy is independent, avoiding bugs from shared references common in classes.

3. Final Answer:

   Structs provide automatic copying, preventing accidental shared changes in user data -> Option B

4. Quick Check:

   Struct copy = safer user profile data [OK]

Hint: Use structs for simple data to avoid shared reference bugs [OK]

Common Mistakes:

• Thinking structs support inheritance like classes
• Confusing reference counting with copying
• Believing structs require manual memory management