Why enums are powerful in Swift - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare an enum named Direction.

Swift

enum [1] {
    case north
    case south
    case east
    case west
}

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

AMove

Bdirection

CDirections

DDirection

Attempts:

3 left

💡 Hint

Common Mistakes

Using lowercase or plural names for enum types.

The enum name should be Direction to follow Swift naming conventions.

2fill in blank

medium

Complete the code to create a variable with the enum value east.

Swift

var currentDirection: Direction = Direction.[1]

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

Aeast

BEast

CNorth

Dwest

Attempts:

3 left

💡 Hint

Common Mistakes

Using uppercase 'East' when the enum case is lowercase 'east'.

Enum cases in Swift start with lowercase by convention. The case is east as per the enum declaration.

3fill in blank

hard

Fix the error in the switch statement to handle all enum cases.

Swift

switch currentDirection {
case .north:
    print("Going north")
case .south:
    print("Going south")
case [1]:
    print("Going east")
default:
    print("Unknown direction")
}

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

A.west

B.east

Ceast

Dwest

Attempts:

3 left

💡 Hint

Common Mistakes

Using case without dot notation or missing cases.

The missing case is .east to cover the east direction in the switch.

4fill in blank

hard

Fill both blanks to create an enum with associated values and assign it.

Swift

enum Barcode {
    case upc(Int, Int, Int, Int)
    case qrCode(String)
}

var productBarcode = Barcode.[1]([2])

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

AqrCode

B"ABCDEFGHIJKLMNOP"

Cupc

D12345, 67890, 1112, 1314

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up case names or providing wrong value types.

The enum case upc takes four integer values as associated values.

5fill in blank

hard

Fill all three blanks to create a recursive enum and use it.

Swift

indirect enum ArithmeticExpression {
    case number(Int)
    case addition([1], [2])
    case multiplication([3], ArithmeticExpression)
}

let five = ArithmeticExpression.number(5)

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

AArithmeticExpression

BInt

DNumber

Attempts:

3 left

💡 Hint

Common Mistakes

Using primitive types instead of the enum type for recursion.

The recursive enum uses ArithmeticExpression as the type for its associated values.

Practice

1. What is one main reason enums are powerful in Swift?

easy

A. They group related values clearly and safely.

B. They allow any type of value without restrictions.

C. They automatically generate user interfaces.

D. They replace all classes and structs.

Solution

1. Step 1: Understand enum purpose

   Enums group related values into a clear set, making code safer and easier to read.

2. Step 2: Compare options

   Options A, B, and C describe features not true for enums. Only They group related values clearly and safely. correctly states their main power.

3. Final Answer:

   They group related values clearly and safely. -> Option A

4. Quick Check:

   Enums group related values = D [OK]

Hint: Enums group related values safely and clearly [OK]

Common Mistakes:

• Thinking enums allow any value type without limits
• Confusing enums with UI components
• Believing enums replace classes and structs

2. Which of the following is the correct syntax to define an enum in Swift?

easy

A. enum Direction: String { north, south, east, west }

B. enum Direction = { north, south, east, west }

C. enum Direction { north; south; east; west }

D. enum Direction { case north, south, east, west }

Solution

1. Step 1: Recall enum syntax

   In Swift, enums use the keyword 'enum' followed by cases declared with 'case' keyword separated by commas.

2. Step 2: Check each option

   enum Direction { case north, south, east, west } uses correct syntax. enum Direction = { north, south, east, west } uses '=' which is invalid. enum Direction: String { north, south, east, west } misses 'case' keyword. enum Direction { north; south; east; west } uses semicolons incorrectly.

3. Final Answer:

   enum Direction { case north, south, east, west } -> Option D

4. Quick Check:

   Correct enum syntax uses 'case' keyword = C [OK]

Hint: Remember enum cases start with 'case' keyword [OK]

Common Mistakes:

• Using '=' instead of '{ }' for enum body
• Omitting 'case' keyword before cases
• Separating cases with semicolons instead of commas

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

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

let outcome = Result.success("Done")
switch outcome {
case .success(let message):
    print("Success: \(message)")
case .failure(let error):
    print("Failure: \(error)")
}

medium

A. Success: error

B. Failure: Done

C. Success: Done

D. Compilation error

Solution

1. Step 1: Understand enum with associated values

   The enum Result has two cases with associated String values. The variable 'outcome' is assigned .success("Done").

2. Step 2: Analyze switch statement

   The switch matches .success case, extracts 'message' as "Done", and prints "Success: Done".

3. Final Answer:

   Success: Done -> Option C

4. Quick Check:

   Matching .success prints message = A [OK]

Hint: Match enum cases with associated values carefully [OK]

Common Mistakes:

• Confusing success and failure cases
• Forgetting to extract associated values
• Expecting compilation error due to associated values

4. Identify the error in this Swift enum code:

enum Status {
    case ready
    case waiting
    case error(String)
}

let current = Status.error
print(current)

medium

A. Enum cases cannot have associated values.

B. Missing associated value for 'error' case.

C. Cannot print enum values directly.

D. Enum must have raw values.

Solution

1. Step 1: Check enum definition

   The 'error' case requires a String associated value, but 'current' is assigned without one.

2. Step 2: Understand assignment error

   Assigning 'Status.error' without a String causes a compile-time error because associated values are mandatory.

3. Final Answer:

   Missing associated value for 'error' case. -> Option B

4. Quick Check:

   Associated values must be provided = A [OK]

Hint: Provide associated values when required by enum case [OK]

Common Mistakes:

• Assigning enum case with associated value without value
• Thinking enums cannot have associated values
• Assuming printing enum directly causes error

5. Given this enum with associated values, how can you extract the associated String from a variable of type Response?

enum Response {
    case data(String)
    case error(Int, String)
}

let reply = Response.error(404, "Not Found")

Which code snippet correctly extracts the error message?

hard

A. if case let .error(code, message) = reply { print(message) }

B. if reply == .error { print("Error") }

C. switch reply { case .data(let msg): print(msg) default: break }

D. let message = reply.errorMessage

Solution

1. Step 1: Understand enum with multiple associated values

   The 'error' case has two associated values: an Int and a String. To get the message, both must be extracted.

2. Step 2: Analyze extraction methods

   if case let .error(code, message) = reply { print(message) } uses pattern matching with 'if case let' to extract both values and print the message. Options A, C, and D are invalid syntax or incomplete.

3. Final Answer:

   if case let .error(code, message) = reply { print(message) } -> Option A

4. Quick Check:

   Pattern match to extract associated values = B [OK]

Hint: Use 'if case let' to extract associated values from enums [OK]

Common Mistakes:

• Trying to compare enum with associated values directly
• Ignoring associated values in switch or if
• Assuming enum has properties like 'errorMessage'