Associated values per case in Swift - Mini Project: Build & Apply

Using Associated Values in Swift Enums

📖 Scenario: Imagine you are building a simple app to track different types of notifications a user can receive. Each notification type can carry extra information.

🎯 Goal: You will create an enum with associated values to represent different notification types and then write code to handle them.

📋 What You'll Learn

Create an enum called Notification with cases that have associated values

Add a variable to hold a sample notification

Use a switch statement to extract and print the associated values

Print the final message describing the notification

💡 Why This Matters

🌍 Real World

Enums with associated values are useful to represent different types of data that share a category but carry extra information, like notifications, messages, or API responses.

💼 Career

Understanding enums with associated values is important for Swift developers building iOS apps, as it helps write clear and safe code for handling varied data types.

1

Create the Notification enum with associated values

Create an enum called Notification with these cases and associated values exactly: message(String), friendRequest(from: String), and photoLike(photoID: Int, liker: String).

Swift

# Your code here

Hint

Use enum keyword and define cases with parentheses for associated values.

2

Create a variable with a sample notification

Create a variable called notification and assign it the Notification.friendRequest(from: "Alice") value.

Swift

enum Notification {
    case message(String)
    case friendRequest(from: String)
    case photoLike(photoID: Int, liker: String)
}

# Your code here

Hint

Use var notification = Notification.friendRequest(from: "Alice") exactly.

3

Use a switch to handle the notification and extract associated values

Write a switch statement on notification with cases for .message(let text), .friendRequest(let from), and .photoLike(let photoID, let liker). Inside each case, create a variable description with a string describing the notification using the associated values.

Swift

enum Notification {
    case message(String)
    case friendRequest(from: String)
    case photoLike(photoID: Int, liker: String)
}

var notification = Notification.friendRequest(from: "Alice")

switch notification {
    // Your code here
}

Hint

Use switch notification and pattern match each case with let to get associated values.

4

Print the notification description

Write a print statement to display the description variable.

Swift

enum Notification {
    case message(String)
    case friendRequest(from: String)
    case photoLike(photoID: Int, liker: String)
}

var notification = Notification.friendRequest(from: "Alice")

var description = ""
switch notification {
case .message(let text):
    description = "Message: \(text)"
case .friendRequest(let from):
    description = "Friend request from \(from)"
case .photoLike(let photoID, let liker):
    description = "Photo \(photoID) liked by \(liker)"
}

print(description)  # Your code here

Hint

Use print(description) to show the message.

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