Associated values per case in Swift - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of enum with associated values

What is the output of this Swift code?

Swift

enum Result {
    case success(data: String)
    case failure(errorCode: Int)
}

let response = Result.success(data: "File loaded")
switch response {
case .success(let data):
    print("Success: \(data)")
case .failure(let code):
    print("Error code: \(code)")
}

A Compilation error

B Error code: 0

C Success: data

D Success: File loaded

💡 Hint

Look at which case is assigned to the variable and what the associated value is.

The enum instance is created with the success case and the associated value "File loaded". The switch matches .success and prints the associated data.

❓ Predict Output

intermediate

Extracting multiple associated values

What will this Swift code print?

Swift

enum Shape {
    case rectangle(width: Int, height: Int)
    case circle(radius: Int)
}

let shape = Shape.rectangle(width: 5, height: 10)
switch shape {
case .rectangle(let w, let h):
    print("Area: \(w * h)")
case .circle(let r):
    print("Area: \(3.14 * Double(r * r))")
}

A Area: 50

B Area: 15

C Area: 78.5

D Runtime error

💡 Hint

Calculate the area of the rectangle using width and height.

The shape is a rectangle with width 5 and height 10, so area is 5 * 10 = 50.

🔧 Debug

advanced

Identify the error with associated values

What error does this Swift code produce?

Swift

enum Device {
    case phone(model: String)
    case tablet
}

let myDevice = Device.phone(model: "iPhone 14")
switch myDevice {
case .phone:
    print("Phone detected")
case .tablet:
    print("Tablet detected")
}

A No error, prints 'Phone detected'

B Error: Missing default case in switch

C Error: Associated value 'model' not extracted in case pattern

D Runtime crash due to missing associated value

💡 Hint

Check if the associated value is handled in the switch case pattern.

The case .phone has an associated value 'model' but the switch case pattern does not extract it, causing a compiler error.

🧠 Conceptual

advanced

Understanding associated values in enums

Which statement about Swift enums with associated values is true?

A All cases must have the same associated value types.

B Each case can store different types and amounts of associated values.

C Associated values must be constants and cannot be extracted.

D Enums with associated values cannot be used in switch statements.

💡 Hint

Think about flexibility of enum cases with associated values.

Swift enums allow each case to have zero or more associated values of any type, and these can differ between cases.

❓ Predict Output

expert

Output of nested associated values in enum

What is the output of this Swift code?

Swift

enum Response {
    case success(data: (id: Int, message: String))
    case failure(error: String)
}

let result = Response.success(data: (id: 101, message: "OK"))
switch result {
case .success(let data):
    print("ID: \(data.id), Message: \(data.message)")
case .failure(let error):
    print("Error: \(error)")
}

A ID: 101, Message: OK

B Error: OK

C ID: (101, "OK"), Message: nil

D Compilation error due to tuple usage

💡 Hint

Look at how the tuple is used as an associated value and accessed.

The success case has a tuple with named elements. The switch extracts the tuple and prints its fields.

Practice

1. What is the main purpose of associated values in Swift enums?

easy

A. To store extra data with each enum case

B. To define multiple enums in one declaration

C. To create functions inside enums

D. To inherit properties from other enums

Solution

1. Step 1: Understand enum cases

   Enum cases represent fixed options, but sometimes need extra data.

2. Step 2: Role of associated values

   Associated values let each case carry extra information, like a label or number.

3. Final Answer:

   To store extra data with each enum case -> Option A

4. Quick Check:

   Associated values = extra data per case [OK]

Hint: Think: extra info stored inside enum cases [OK]

Common Mistakes:

• Confusing associated values with raw values
• Thinking enums can inherit properties
• Believing enums can contain functions only

2. Which of the following is the correct syntax to define an enum case with an associated value of type String?

easy

A. case name -> String

B. case name(String)

C. case name: String

D. case name = String

Solution

1. Step 1: Recall enum case syntax with associated values

   Associated values use parentheses after the case name with the type inside.

2. Step 2: Match syntax options

   Only 'case name(String)' uses parentheses correctly for associated values.

3. Final Answer:

   case name(String) -> Option B

4. Quick Check:

   Parentheses hold associated value type [OK]

Hint: Use parentheses for associated value types [OK]

Common Mistakes:

• Using colon instead of parentheses
• Using equals sign for associated values
• Using arrow notation incorrectly

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

enum Result {
    case success(String)
    case failure(Int)
}

let response = Result.success("Done")
switch response {
case .success(let message):
    print(message)
case .failure(let code):
    print("Error code: \(code)")
}

medium

A. Error code: Done

B. Compilation error

C. Error code: 0

D. Done

Solution

1. Step 1: Identify enum case used

   The variable 'response' is assigned 'Result.success("Done")'.

2. Step 2: Switch matches .success case

   The switch matches '.success(let message)' and prints the message string.

3. Final Answer:

   Done -> Option D

4. Quick Check:

   Matching case prints associated string [OK]

Hint: Match enum case to print its associated value [OK]

Common Mistakes:

• Confusing success and failure cases
• Expecting error code instead of message
• Thinking code will not compile

4. Identify the error in this Swift enum usage:

enum Device {
    case phone(model: String)
    case tablet(model: String)
}

let myDevice = Device.phone("iPhone")

medium

A. Missing parentheses around associated value

B. Enum cases cannot have associated values

C. Cannot assign associated value without label

D. Incorrect enum declaration syntax

Solution

1. Step 1: Check enum case declaration

   Cases use labeled associated values: 'phone(model: String)'.

2. Step 2: Check enum instance assignment

   Assigning 'Device.phone("iPhone")' omits the label 'model:'.

3. Final Answer:

   Cannot assign associated value without label -> Option C

4. Quick Check:

   Labeled associated values require labels on assignment [OK]

Hint: Use labels when enum cases define labeled associated values [OK]

Common Mistakes:

• Ignoring labels in associated values
• Thinking parentheses are missing
• Believing enums can't have associated values

5. Given this enum with multiple associated values:

enum Message {
    case text(String, Int)
    case image(url: String, size: (width: Int, height: Int))
}

let msg = Message.image(url: "photo.png", size: (width: 100, height: 200))
switch msg {
case .text(let content, let length):
    print("Text: \(content), length: \(length)")
case .image(let url, let size):
    print("Image URL: \(url), size: \(size.width)x\(size.height)")
}

What will be printed?

hard

A. Image URL: photo.png, size: 100x200

B. Text: photo.png, length: 100

C. Image URL: photo.png, size: (100, 200)

D. Compilation error due to tuple

Solution

1. Step 1: Identify enum case and associated values

   Variable 'msg' is assigned '.image' with url and size tuple.

2. Step 2: Switch matches .image case and prints values

   Print statement accesses url and tuple's width and height correctly.

3. Final Answer:

   Image URL: photo.png, size: 100x200 -> Option A

4. Quick Check:

   Tuple values accessed with dot notation [OK]

Hint: Access tuple parts with dot notation inside switch [OK]

Common Mistakes:

• Printing tuple as whole instead of parts
• Confusing .text and .image cases
• Expecting compilation error from tuple