Enum methods and computed properties in Swift - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of enum method with computed property

What is the output of this Swift code?

Swift

enum Direction {
    case north, south, east, west
    
    var isVertical: Bool {
        return self == .north || self == .south
    }
    
    func description() -> String {
        return isVertical ? "Vertical" : "Horizontal"
    }
}

let dir = Direction.east
print(dir.description())

A "Vertical"

B "north"

C Compilation error

D "Horizontal"

💡 Hint

Check how the computed property 'isVertical' is defined and used in the method.

The enum Direction has a computed property 'isVertical' that returns true only for .north and .south. Since 'dir' is .east, 'isVertical' is false, so description() returns "Horizontal".

❓ Predict Output

intermediate

Computed property with associated values

What will be printed by this Swift code?

Swift

enum Result {
    case success(Int)
    case failure(String)
    
    var message: String {
        switch self {
        case .success(let code):
            return "Success with code \(code)"
        case .failure(let error):
            return "Failed: \(error)"
        }
    }
}

let res = Result.failure("Network error")
print(res.message)

A "Failed: Network error"

B "Success with code 0"

C Runtime error

D "Failed: nil"

💡 Hint

Look at how the associated value is extracted in the computed property.

The enum case is .failure with associated value "Network error", so the computed property returns "Failed: Network error".

🔧 Debug

advanced

Identify the error in enum method

What error does this Swift code produce when compiled?

Swift

enum Status {
    case ready, waiting
    
    func isReady() -> Bool {
        switch self {
        case .ready:
            return true
        case .waiting
            return false
        }
    }
}

A Runtime error: Missing return statement

B TypeError: Cannot return Bool from function

C SyntaxError: Missing colon after 'case .waiting'

D No error, compiles fine

💡 Hint

Check the switch case syntax carefully.

The case '.waiting' is missing a colon ':' after it, causing a syntax error.

❓ Predict Output

advanced

Computed property returning different types

What is the output of this Swift code?

Swift

enum Measurement {
    case weight(Double)
    case count(Int)
    
    var description: String {
        switch self {
        case .weight(let w):
            return "Weight: \(w) kg"
        case .count(let c):
            return "Count: \(c) items"
        }
    }
}

let m = Measurement.weight(3.5)
print(m.description)

A Compilation error: mismatched types

B "Weight: 3.5 kg"

C "Count: 3.5 items"

D "Weight: 3 kg"

💡 Hint

Check the associated value type and string interpolation.

The enum case is .weight with value 3.5, so the description returns "Weight: 3.5 kg".

🧠 Conceptual

expert

Why use computed properties in enums?

Which of the following best explains why computed properties are useful in Swift enums?

A They enable adding dynamic behavior or derived values based on the enum case and its associated values.

B They allow storing additional data inside enum cases without associated values.

C They make enums mutable so their cases can change at runtime.

D They automatically generate raw values for enum cases.

💡 Hint

Think about what computed properties do in general.

Computed properties let you add dynamic behavior or calculate values based on the enum case and its associated data, without storing extra data.

Practice

1. What is the purpose of adding methods to an enum in Swift?

easy

A. To inherit properties from other enums

B. To store additional data inside enum cases

C. To perform actions or calculations related to enum cases

D. To convert enums into classes automatically

Solution

1. Step 1: Understand enum methods

   Enum methods allow you to add functions that perform tasks related to the enum's cases.

2. Step 2: Differentiate from other enum features

   Enums do not store extra data like classes; methods help organize related actions.

3. Final Answer:

   To perform actions or calculations related to enum cases -> Option C

4. Quick Check:

   Enum methods = perform actions [OK]

Hint: Methods in enums perform actions tied to cases [OK]

Common Mistakes:

• Thinking enums can inherit from other enums
• Confusing methods with stored properties
• Assuming enums convert to classes automatically

2. Which of the following is the correct syntax to declare a computed property inside an enum in Swift?

easy

A. static var description: String = "Example"

B. func description() -> String { return "Example" }

C. let description = "Example"

D. var description: String { return "Example" }

Solution

1. Step 1: Identify computed property syntax

   Computed properties use var with a code block returning a value, like var name: Type { ... }.

2. Step 2: Check options

   var description: String { return "Example" } matches computed property syntax; B is a method, C is a stored property, D is a static stored property.

3. Final Answer:

   var description: String { return "Example" } -> Option D

4. Quick Check:

   Computed property syntax = var with braces [OK]

Hint: Computed properties use var with braces returning a value [OK]

Common Mistakes:

• Using func instead of var for computed properties
• Declaring computed properties as let constants
• Confusing static stored properties with computed ones

3. Consider this Swift enum with a computed property and method:

enum Direction {
    case north, south, east, west

    var isVertical: Bool {
        return self == .north || self == .south
    }

    func description() -> String {
        switch self {
        case .north: return "Up"
        case .south: return "Down"
        case .east: return "Right"
        case .west: return "Left"
        }
    }
}

let dir = Direction.east
print(dir.isVertical)
print(dir.description())

What is the output?

medium

A. false
Right

B. true
Right

C. false
East

D. true
East

Solution

1. Step 1: Evaluate computed property isVertical

   For Direction.east, isVertical checks if east == north or south, which is false.

2. Step 2: Evaluate description() method

   Switch on east returns "Right" string.

3. Final Answer:

   false Right -> Option A

4. Quick Check:

   east isVertical = false, description = Right [OK]

Hint: Check enum case matches in computed property and switch [OK]

Common Mistakes:

• Assuming east is vertical
• Confusing method return values with case names
• Forgetting to call method with parentheses

4. This Swift enum code has an error:

enum Status {
    case success, failure

    var message: String {
        switch self {
        case .success:
            return "Success"
        case .failure
            return "Failure"
        }
    }
}

What is the error and how to fix it?

medium

A. Computed property must be a function; change to func message() -> String

B. Missing colon after case .failure; add ':' after .failure

C. Enum cases must have raw values; add raw values to cases

D. Return statements are not allowed in computed properties; remove returns

Solution

1. Step 1: Identify syntax error in switch cases

   Case .failure is missing a colon ':' after it, causing a syntax error.

2. Step 2: Fix the syntax

   Add ':' after case .failure to correct the switch syntax.

3. Final Answer:

   Missing colon after case .failure; add ':' after .failure -> Option B

4. Quick Check:

   Switch case syntax requires ':' [OK]

Hint: Switch cases must end with a colon ':' [OK]

Common Mistakes:

• Thinking computed properties need func keyword
• Adding raw values unnecessarily
• Removing return statements inside computed properties

5. You want to create an enum Light with cases red, yellow, and green. Add a computed property time that returns the duration in seconds for each light: red = 30, yellow = 5, green = 25. Also add a method next() that returns the next light in the traffic cycle (red -> green -> yellow -> red). Which implementation is correct?

hard

A. enum Light {
case red, yellow, green

var time: Int {
switch self {
case .red: return 30
case .yellow: return 5
case .green: return 25
}
}

func next() -> Light {
switch self {
case .red: return .green
case .green: return .yellow
case .yellow: return .red
}
}
}

B. enum Light {
case red, yellow, green

func time() -> Int {
if self == .red { return 30 }
else if self == .yellow { return 5 }
else { return 25 }
}

func next() -> Light {
if self == .red { return .yellow }
else if self == .yellow { return .green }
else { return .red }
}
}

C. enum Light {
case red, yellow, green

var time: Int {
if self == .red { return 30 }
else if self == .yellow { return 5 }
else { return 25 }
}

func next() -> Light {
switch self {
case .red: return .yellow
case .yellow: return .green
case .green: return .red
}
}
}

D. enum Light {
case red, yellow, green

var time: Int {
switch self {
case .red: return 25
case .yellow: return 30
case .green: return 5
}
}

func next() -> Light {
switch self {
case .red: return .green
case .green: return .yellow
case .yellow: return .red
}
}
}

Solution

1. Step 1: Check computed property time values

   enum Light { case red, yellow, green var time: Int { switch self { case .red: return 30 case .yellow: return 5 case .green: return 25 } } func next() -> Light { switch self { case .red: return .green case .green: return .yellow case .yellow: return .red } } } correctly returns 30 for red, 5 for yellow, and 25 for green as required.

2. Step 2: Check next() method cycle order

   enum Light { case red, yellow, green var time: Int { switch self { case .red: return 30 case .yellow: return 5 case .green: return 25 } } func next() -> Light { switch self { case .red: return .green case .green: return .yellow case .yellow: return .red } } } cycles red -> green -> yellow -> red, matching the problem statement.

3. Final Answer:

   enum Light { case red, yellow, green var time: Int { switch self { case .red: return 30 case .yellow: return 5 case .green: return 25 } } func next() -> Light { switch self { case .red: return .green case .green: return .yellow case .yellow: return .red } } } -> Option A

4. Quick Check:

   Correct time values and cycle order = enum Light { case red, yellow, green var time: Int { switch self { case .red: return 30 case .yellow: return 5 case .green: return 25 } } func next() -> Light { switch self { case .red: return .green case .green: return .yellow case .yellow: return .red } } } [OK]

Hint: Match switch cases exactly to problem requirements [OK]

Common Mistakes:

• Mixing up time values for colors
• Incorrect next() cycle order
• Using func instead of computed property for time