Enum methods and computed properties in Swift - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a computed property that returns a description for the enum case.

Swift

enum Direction {
    case north, south, east, west
    var description: String {
        switch self {
        case .north: return "Going [1]"
        case .south: return "Going south"
        case .east: return "Going east"
        case .west: return "Going west"
        }
    }
}

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

Aleft

Bup

Cnorth

Dright

Attempts:

3 left

💡 Hint

Common Mistakes

Using a direction word that doesn't match the case name.

Leaving the placeholder blank.

The computed property returns a string describing the enum case. For the .north case, it should return "Going north".

2fill in blank

medium

Complete the method to return true if the direction is vertical (north or south).

Swift

enum Direction {
    case north, south, east, west
    func isVertical() -> Bool {
        return self == .[1] || self == .south
    }
}

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

Aup

Beast

Cwest

Dnorth

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'east' or 'west' which are horizontal directions.

Using a non-existent case like 'up'.

The method checks if the direction is vertical by comparing to .north or .south. The blank must be 'north'.

3fill in blank

hard

Fix the error in the method that returns the opposite direction.

Swift

enum Direction {
    case north, south, east, west
    func opposite() -> Direction {
        switch self {
        case .north: return .[1]
        case .south: return .north
        case .east: return .west
        case .west: return .east
        }
    }
}

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

Asouth

Bnorth

Ceast

Dwest

Attempts:

3 left

💡 Hint

Common Mistakes

Returning .north for the .north case causing no change.

Returning east or west which are not opposites of north.

The opposite of north is south, so the method should return .south for the .north case.

4fill in blank

hard

Fill both blanks to create a computed property that returns true if the direction is horizontal.

Swift

enum Direction {
    case north, south, east, west
    var isHorizontal: Bool {
        return self == .[1] || self == .[2]
    }
}

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

Aeast

Bnorth

Cwest

Dsouth

Attempts:

3 left

💡 Hint

Common Mistakes

Using north or south which are vertical directions.

Swapping the order of east and west is acceptable but must match correct_answer.

Horizontal directions are east and west, so the computed property returns true if self is .east or .west.

5fill in blank

hard

Fill all three blanks to create a method that returns a string with the direction and its opposite.

Swift

enum Direction {
    case north, south, east, west
    func descriptionWithOpposite() -> String {
        let opposite: Direction
        switch self {
        case .north: opposite = .[1]
        case .south: opposite = .north
        case .east: opposite = .west
        case .west: opposite = .east
        }
        return "\([2]\) is opposite to \([3]\)"
    }
}

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

Asouth

Bself

Copposite

Dnorth

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong opposite direction for .north.

Using literal strings instead of variables in the return statement.

The method assigns opposite for .north as .south, then returns a string using 'self' and 'opposite' to describe the relation.

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