Associated values per case in Swift - Cheat Sheet & Quick Revision

Recall & Review

beginner

What are associated values in Swift enums?

Associated values let each case of an enum store additional data of different types, like carrying extra information with that case.

beginner

How do you define an enum case with associated values in Swift?

You add parentheses after the case name and list the types of values it holds, for example: case success(data: String).

intermediate

How do you extract associated values from an enum case in Swift?

Use a switch statement with pattern matching to bind the associated values to constants or variables.

beginner

Can different cases of the same enum have different types of associated values?

Yes, each case can have its own unique types and number of associated values.

beginner

Example: What does this Swift code do?

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

It defines an enum Result with two cases: success holding a String, and failure holding an Int as associated values.

What is the purpose of associated values in Swift enums?

A To create constants

B To inherit from other enums

C To define functions inside enums

D To store extra data with each enum case

Associated values let enum cases carry extra data, like a package with information.

How do you declare an enum case with associated values?

A case name = Type

B case name(Type)

C case name: Type

D case name -> Type

You write the case name followed by parentheses with the type(s) inside, e.g., case success(String).

Which Swift statement is best to get associated values from an enum case?

A if-else

B for loop

C switch

D while loop

A switch statement with pattern matching extracts associated values easily.

Can two enum cases have different types of associated values?

A Yes, each case can differ

B No, all must be the same

C Only if they are strings

D Only if they have no values

Each enum case can have its own unique associated value types.

What does this enum case mean?
case error(code: Int, message: String)

A An error case with an Int and String stored

B A function named error

C A constant named error

D A variable named error

It defines an enum case error that holds an Int and a String as associated values.

Explain what associated values are in Swift enums and how you use them.

Think about how each enum case can carry extra information.

Describe how you would handle different associated values for multiple enum cases in Swift.

Consider how to get the data out when you check the enum case.

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